diff --git a/crates/irtt-cli/src/main.rs b/crates/irtt-cli/src/main.rs
index 202956b..e23eb0d 100644
--- a/crates/irtt-cli/src/main.rs
+++ b/crates/irtt-cli/src/main.rs
@@ -72,7 +72,7 @@ fn run(args: CliArgs, shutdown_requested: &AtomicBool) -> Result<(), Box<dyn std
         return Ok(());
     }
 
-    let open = client.open(ClientTimestamp::now())?;
+    let open = client.open()?;
     output.print_event(open_event(&open))?;
 
     let mut interrupted = false;
diff --git a/crates/irtt-client/src/client.rs b/crates/irtt-client/src/client.rs
index bd7734a..711da85 100644
--- a/crates/irtt-client/src/client.rs
+++ b/crates/irtt-client/src/client.rs
@@ -73,7 +73,7 @@ impl Client {
         })
     }
 
-    pub fn open(&mut self, now: ClientTimestamp) -> Result<OpenOutcome, ClientError> {
+    pub fn open(&mut self) -> Result<OpenOutcome, ClientError> {
         match self.phase {
             ClientPhase::Connected => {}
             ClientPhase::Open { .. } => return Err(ClientError::AlreadyOpen),
@@ -81,10 +81,44 @@ impl Client {
             ClientPhase::NoTestCompleted => return Err(ClientError::AlreadyCompleted),
         }
 
-        let outcome = self.open_inner(now);
+        let outcome = (|| -> Result<OpenOutcome, ClientError> {
+            let request = OpenRequest {
+                params: self.requested.clone(),
+                close: self.config.run_mode == RunMode::NoTest,
+            };
+
+            let packet = encode_open_request(&request, self.config.hmac_key.as_deref())?;
+            let mut buf = [0_u8; MAX_OPEN_PACKET_SIZE];
+
+            for timeout in &self.config.open_timeouts {
+                self.socket.set_read_timeout(Some(*timeout))?;
+                self.socket.send(&packet)?;
+
+                match self.socket.recv(&mut buf) {
+                    Ok(size) => {
+                        let reply = irtt_proto::decode_open_reply(
+                            &buf[..size],
+                            self.config.hmac_key.as_deref(),
+                        )?;
+
+                        return self.accept_open_reply(reply, ClientTimestamp::now());
+                    }
+                    Err(err)
+                        if matches!(
+                            err.kind(),
+                            io::ErrorKind::WouldBlock | io::ErrorKind::TimedOut
+                        ) => {}
+                    Err(err) => return Err(ClientError::Socket(err)),
+                }
+            }
+
+            Err(ClientError::OpenTimeout)
+        })();
+
         let restore = self
             .socket
             .set_read_timeout(self.config.socket_config.recv_timeout);
+
         match (outcome, restore) {
             (Ok(outcome), Ok(())) => Ok(outcome),
             (Ok(_), Err(source)) => Err(ClientError::ReadTimeoutRestore { source }),
@@ -93,38 +127,6 @@ impl Client {
         }
     }
 
-    fn open_inner(&mut self, _now: ClientTimestamp) -> Result<OpenOutcome, ClientError> {
-        let request = OpenRequest {
-            params: self.requested.clone(),
-            close: self.config.run_mode == RunMode::NoTest,
-        };
-        let packet = encode_open_request(&request, self.config.hmac_key.as_deref())?;
-        let mut buf = [0_u8; MAX_OPEN_PACKET_SIZE];
-
-        for timeout in &self.config.open_timeouts {
-            self.socket.set_read_timeout(Some(*timeout))?;
-            self.socket.send(&packet)?;
-
-            match self.socket.recv(&mut buf) {
-                Ok(size) => {
-                    let reply = irtt_proto::decode_open_reply(
-                        &buf[..size],
-                        self.config.hmac_key.as_deref(),
-                    )?;
-                    return self.accept_open_reply(reply, ClientTimestamp::now());
-                }
-                Err(err)
-                    if matches!(
-                        err.kind(),
-                        io::ErrorKind::WouldBlock | io::ErrorKind::TimedOut
-                    ) => {}
-                Err(err) => return Err(ClientError::Socket(err)),
-            }
-        }
-
-        Err(ClientError::OpenTimeout)
-    }
-
     pub fn close(&mut self, now: ClientTimestamp) -> Result<Vec<ClientEvent>, ClientError> {
         let token = match self.phase {
             ClientPhase::Open { token } => token,
diff --git a/crates/irtt-client/src/client/tests/close.rs b/crates/irtt-client/src/client/tests/close.rs
index 63b8962..bedd7d9 100644
--- a/crates/irtt-client/src/client/tests/close.rs
+++ b/crates/irtt-client/src/client/tests/close.rs
@@ -11,10 +11,10 @@ fn open_fails_after_close() {
         let _ = recv_request(&socket, &tx);
     });
     let mut client = Client::connect(default_test_config(server.addr)).unwrap();
-    assert_open_started(client.open(ClientTimestamp::now()).unwrap());
+    assert_open_started(client.open().unwrap());
     client.close(ClientTimestamp::now()).unwrap();
     assert!(matches!(
-        client.open(ClientTimestamp::now()),
+        client.open(),
         Err(ClientError::AlreadyClosed)
     ));
     server.join();
@@ -31,7 +31,7 @@ fn close_sends_one_close_packet_with_negotiated_token() {
         let _ = recv_request(&socket, &tx);
     });
     let mut client = Client::connect(default_test_config(server.addr)).unwrap();
-    assert_open_started(client.open(ClientTimestamp::now()).unwrap());
+    assert_open_started(client.open().unwrap());
     let events = client.close(ClientTimestamp::now()).unwrap();
     assert_eq!(events.len(), 1);
     let packets: Vec<_> = server.rx.iter().take(2).collect();
@@ -62,7 +62,7 @@ fn send_probe_fails_after_close() {
         }
     });
     let mut client = Client::connect(default_test_config(server.addr)).unwrap();
-    assert_open_started(client.open(ClientTimestamp::now()).unwrap());
+    assert_open_started(client.open().unwrap());
     client.close(ClientTimestamp::now()).unwrap();
     assert!(matches!(
         client.send_probe(),
@@ -84,7 +84,7 @@ fn close_clears_timed_out_metadata() {
         ..default_test_config(server.addr)
     };
     let mut client = Client::connect(config).unwrap();
-    assert_open_started(client.open(ClientTimestamp::now()).unwrap());
+    assert_open_started(client.open().unwrap());
 
     client.send_probe().unwrap();
     thread::sleep(Duration::from_millis(60));
@@ -132,7 +132,7 @@ fn close_flagged_echo_reply_emits_reply_then_closes_without_sending_close() {
         ..default_test_config(server.addr)
     };
     let mut client = Client::connect(config).unwrap();
-    assert_open_started(client.open(ClientTimestamp::now()).unwrap());
+    assert_open_started(client.open().unwrap());
     client.send_probe().unwrap();
 
     let events = client.recv_once().unwrap();
diff --git a/crates/irtt-client/src/client/tests/dscp.rs b/crates/irtt-client/src/client/tests/dscp.rs
index 80e2d09..f1bff80 100644
--- a/crates/irtt-client/src/client/tests/dscp.rs
+++ b/crates/irtt-client/src/client/tests/dscp.rs
@@ -26,7 +26,7 @@ fn normal_open_applies_negotiated_dscp_after_open_and_close_clears_it() {
         socket_traffic_class(&client.socket, client.remote).unwrap() & 0xfc,
         0
     );
-    assert_open_started(client.open(ClientTimestamp::now()).unwrap());
+    assert_open_started(client.open().unwrap());
     assert_eq!(
         socket_traffic_class(&client.socket, client.remote).unwrap() & 0xfc,
         184
@@ -58,7 +58,7 @@ fn normal_open_uses_negotiated_dscp_not_requested_dscp() {
     config.negotiation_policy = NegotiationPolicy::Loose;
     let mut client = Client::connect(config).unwrap();
 
-    let negotiated = assert_open_started(client.open(ClientTimestamp::now()).unwrap());
+    let negotiated = assert_open_started(client.open().unwrap());
     assert_eq!(negotiated.params.dscp, 0);
     assert_eq!(
         socket_traffic_class(&client.socket, client.remote).unwrap(),
diff --git a/crates/irtt-client/src/client/tests/hmac.rs b/crates/irtt-client/src/client/tests/hmac.rs
index 2afcc8e..38b274f 100644
--- a/crates/irtt-client/src/client/tests/hmac.rs
+++ b/crates/irtt-client/src/client/tests/hmac.rs
@@ -14,7 +14,7 @@ fn hmac_open_success() {
     });
     config.server_addr = server.addr.to_string();
     let mut client = Client::connect(config).unwrap();
-    assert_open_started(client.open(ClientTimestamp::now()).unwrap());
+    assert_open_started(client.open().unwrap());
     server.join();
 }
 
@@ -32,7 +32,7 @@ fn hmac_open_rejects_missing_hmac() {
     config.server_addr = server.addr.to_string();
     let mut client = Client::connect(config).unwrap();
     assert!(matches!(
-        client.open(ClientTimestamp::now()),
+        client.open(),
         Err(ClientError::Protocol(
             irtt_proto::ProtoError::HmacPresenceMismatch
         ))
@@ -55,7 +55,7 @@ fn hmac_open_rejects_bad_hmac() {
     config.server_addr = server.addr.to_string();
     let mut client = Client::connect(config).unwrap();
     assert!(matches!(
-        client.open(ClientTimestamp::now()),
+        client.open(),
         Err(ClientError::Protocol(irtt_proto::ProtoError::BadHmac))
     ));
     server.join();
@@ -76,7 +76,7 @@ fn hmac_close_packet_includes_valid_hmac() {
     });
     config.server_addr = server.addr.to_string();
     let mut client = Client::connect(config).unwrap();
-    assert_open_started(client.open(ClientTimestamp::now()).unwrap());
+    assert_open_started(client.open().unwrap());
     client.close(ClientTimestamp::now()).unwrap();
     let packets: Vec<_> = server.rx.iter().take(2).collect();
     let close = &packets[1];
@@ -125,7 +125,7 @@ fn bad_hmac_reply_is_dropped() {
         ..default_test_config(server.addr)
     };
     let mut client = Client::connect(config).unwrap();
-    assert_open_started(client.open(ClientTimestamp::now()).unwrap());
+    assert_open_started(client.open().unwrap());
     client.send_probe().unwrap();
     thread::sleep(Duration::from_millis(30));
     let events = client.recv_once().unwrap();
@@ -174,7 +174,7 @@ fn hmac_echo_request_reply_works() {
         ..default_test_config(server.addr)
     };
     let mut client = Client::connect(config).unwrap();
-    assert_open_started(client.open(ClientTimestamp::now()).unwrap());
+    assert_open_started(client.open().unwrap());
     client.send_probe().unwrap();
     thread::sleep(Duration::from_millis(50));
     let events = client.recv_once().unwrap();
diff --git a/crates/irtt-client/src/client/tests/no_test.rs b/crates/irtt-client/src/client/tests/no_test.rs
index fb6a195..90a3db1 100644
--- a/crates/irtt-client/src/client/tests/no_test.rs
+++ b/crates/irtt-client/src/client/tests/no_test.rs
@@ -8,7 +8,7 @@ fn no_test_open_close_succeeds_on_open_reply_close() {
     let server = no_test_server(params.clone(), 0);
     config.server_addr = server.addr.to_string();
     let mut client = Client::connect(config).unwrap();
-    let negotiated = assert_no_test_completed(client.open(ClientTimestamp::now()).unwrap());
+    let negotiated = assert_no_test_completed(client.open().unwrap());
     assert_eq!(negotiated.params, params);
     assert_eq!(client.negotiated.as_ref(), Some(&negotiated));
     assert!(matches!(
@@ -26,7 +26,7 @@ fn no_test_success_validates_params() {
     let server = no_test_server(params.clone(), 0);
     config.server_addr = server.addr.to_string();
     let mut client = Client::connect(config).unwrap();
-    let negotiated = assert_no_test_completed(client.open(ClientTimestamp::now()).unwrap());
+    let negotiated = assert_no_test_completed(client.open().unwrap());
     assert_eq!(negotiated.params, params);
     server.join();
 }
@@ -40,7 +40,7 @@ fn no_test_rejects_non_close_open_reply() {
     config.server_addr = server.addr.to_string();
     let mut client = Client::connect(config).unwrap();
     assert!(matches!(
-        client.open(ClientTimestamp::now()),
+        client.open(),
         Err(ClientError::UnexpectedNoTestReply)
     ));
     server.join();
@@ -55,7 +55,7 @@ fn no_test_rejects_non_zero_token_with_close_reply() {
     config.server_addr = server.addr.to_string();
     let mut client = Client::connect(config).unwrap();
     assert!(matches!(
-        client.open(ClientTimestamp::now()),
+        client.open(),
         Err(ClientError::NonZeroNoTestToken { token: TOKEN })
     ));
     server.join();
@@ -71,7 +71,7 @@ fn no_test_strict_negotiation_rejects_changed_params() {
     config.server_addr = server.addr.to_string();
     let mut client = Client::connect(config).unwrap();
     assert!(matches!(
-        client.open(ClientTimestamp::now()),
+        client.open(),
         Err(ClientError::NegotiationRejected { .. })
     ));
     server.join();
@@ -87,7 +87,7 @@ fn no_test_loose_negotiation_accepts_restricted_params() {
     let server = no_test_server(params.clone(), 0);
     config.server_addr = server.addr.to_string();
     let mut client = Client::connect(config).unwrap();
-    let negotiated = assert_no_test_completed(client.open(ClientTimestamp::now()).unwrap());
+    let negotiated = assert_no_test_completed(client.open().unwrap());
     assert_eq!(negotiated.params, params);
     server.join();
 }
@@ -100,7 +100,7 @@ fn send_probe_fails_after_no_test_completed() {
     let server = no_test_server(params, 0);
     config.server_addr = server.addr.to_string();
     let mut client = Client::connect(config).unwrap();
-    assert_no_test_completed(client.open(ClientTimestamp::now()).unwrap());
+    assert_no_test_completed(client.open().unwrap());
     assert!(matches!(
         client.send_probe(),
         Err(ClientError::AlreadyCompleted)
@@ -116,9 +116,9 @@ fn open_fails_after_no_test_completed() {
     let server = no_test_server(params, 0);
     config.server_addr = server.addr.to_string();
     let mut client = Client::connect(config).unwrap();
-    assert_no_test_completed(client.open(ClientTimestamp::now()).unwrap());
+    assert_no_test_completed(client.open().unwrap());
     assert!(matches!(
-        client.open(ClientTimestamp::now()),
+        client.open(),
         Err(ClientError::AlreadyCompleted)
     ));
     server.join();
diff --git a/crates/irtt-client/src/client/tests/open.rs b/crates/irtt-client/src/client/tests/open.rs
index 1fea096..cc0a0d9 100644
--- a/crates/irtt-client/src/client/tests/open.rs
+++ b/crates/irtt-client/src/client/tests/open.rs
@@ -18,7 +18,7 @@ fn successful_open_handshake() {
     let server = open_success_server(params.clone());
     let mut client = Client::connect(default_test_config(server.addr)).unwrap();
 
-    let negotiated = assert_open_started(client.open(ClientTimestamp::now()).unwrap());
+    let negotiated = assert_open_started(client.open().unwrap());
     assert_eq!(negotiated.params, params);
     assert!(matches!(client.phase, ClientPhase::Open { token: TOKEN }));
     server.join();
@@ -30,9 +30,9 @@ fn open_fails_when_already_open() {
     let params = params_from_config(&config).unwrap();
     let server = open_success_server(params);
     let mut client = Client::connect(default_test_config(server.addr)).unwrap();
-    assert_open_started(client.open(ClientTimestamp::now()).unwrap());
+    assert_open_started(client.open().unwrap());
     assert!(matches!(
-        client.open(ClientTimestamp::now()),
+        client.open(),
         Err(ClientError::AlreadyOpen)
     ));
     server.join();
@@ -53,7 +53,7 @@ fn open_retries_after_first_timeout() {
         ..default_test_config(server.addr)
     };
     let mut client = Client::connect(config).unwrap();
-    let outcome = client.open(ClientTimestamp::now()).unwrap();
+    let outcome = client.open().unwrap();
     assert_open_started(outcome);
     assert_eq!(server.rx.iter().take(2).count(), 2);
     server.join();
@@ -68,7 +68,7 @@ fn open_timeout_after_all_timeouts() {
     };
     let mut client = Client::connect(config).unwrap();
     assert!(matches!(
-        client.open(ClientTimestamp::now()),
+        client.open(),
         Err(ClientError::OpenTimeout)
     ));
     assert_eq!(server.rx.iter().take(2).count(), 2);
@@ -88,7 +88,7 @@ fn open_restores_configured_read_timeout_after_timeout() {
     };
     let mut client = Client::connect(config).unwrap();
     assert!(matches!(
-        client.open(ClientTimestamp::now()),
+        client.open(),
         Err(ClientError::OpenTimeout)
     ));
 
@@ -108,7 +108,7 @@ fn protocol_version_mismatch_fails() {
     let server = open_success_server(params);
     let mut client = Client::connect(default_test_config(server.addr)).unwrap();
     assert!(matches!(
-        client.open(ClientTimestamp::now()),
+        client.open(),
         Err(ClientError::ProtocolVersionMismatch { received: 2, .. })
     ));
     server.join();
@@ -125,7 +125,7 @@ fn server_rejection_fails_in_normal_mode() {
     });
     let mut client = Client::connect(default_test_config(server.addr)).unwrap();
     assert!(matches!(
-        client.open(ClientTimestamp::now()),
+        client.open(),
         Err(ClientError::ServerRejected)
     ));
     server.join();
diff --git a/crates/irtt-client/src/client/tests/probes_replies.rs b/crates/irtt-client/src/client/tests/probes_replies.rs
index 4be8741..4e90d83 100644
--- a/crates/irtt-client/src/client/tests/probes_replies.rs
+++ b/crates/irtt-client/src/client/tests/probes_replies.rs
@@ -38,7 +38,7 @@ fn send_probe_sends_valid_echo_request() {
         ..default_test_config(server.addr)
     };
     let mut client = Client::connect(config).unwrap();
-    assert_open_started(client.open(ClientTimestamp::now()).unwrap());
+    assert_open_started(client.open().unwrap());
     let events = client.send_probe().unwrap();
     assert_eq!(events.len(), 1);
     match &events[0] {
@@ -89,7 +89,7 @@ fn echo_sent_reports_schedule_and_timer_error() {
         mono: Instant::now(),
         wall: SystemTime::now(),
     };
-    assert_open_started(client.open(start).unwrap());
+    assert_open_started(client.open().unwrap());
     let session_start = client.session.as_ref().unwrap().start_mono;
     assert!(
         session_start >= start.mono,
@@ -131,7 +131,7 @@ fn send_probe_starts_seq_at_zero_and_increments() {
         ..default_test_config(server.addr)
     };
     let mut client = Client::connect(config).unwrap();
-    assert_open_started(client.open(ClientTimestamp::now()).unwrap());
+    assert_open_started(client.open().unwrap());
     client.send_probe().unwrap();
     client.send_probe().unwrap();
     client.send_probe().unwrap();
@@ -172,7 +172,7 @@ fn send_probe_respects_finite_duration_exclusive_end() {
         ..default_test_config(server.addr)
     };
     let mut client = Client::connect(config).unwrap();
-    assert_open_started(client.open(ClientTimestamp::now()).unwrap());
+    assert_open_started(client.open().unwrap());
 
     let session = client.session.as_ref().unwrap();
     let start = session.start_mono;
@@ -225,7 +225,7 @@ fn continuous_duration_keeps_generating_send_deadlines() {
         ..default_test_config(server.addr)
     };
     let mut client = Client::connect(config).unwrap();
-    assert_open_started(client.open(ClientTimestamp::now()).unwrap());
+    assert_open_started(client.open().unwrap());
 
     let start = client.session.as_ref().unwrap().start_mono;
     let interval = Duration::from_millis(500);
@@ -301,7 +301,7 @@ fn send_probe_reports_schedule_overflow() {
         ..default_test_config(server.addr)
     };
     let mut client = Client::connect(config).unwrap();
-    assert_open_started(client.open(ClientTimestamp::now()).unwrap());
+    assert_open_started(client.open().unwrap());
     client.session.as_mut().unwrap().packets_sent = u64::MAX - 1;
 
     assert!(matches!(
@@ -323,7 +323,7 @@ fn send_probe_reports_logical_sequence_counter_overflow() {
         ..default_test_config(server.addr)
     };
     let mut client = Client::connect(config).unwrap();
-    assert_open_started(client.open(ClientTimestamp::now()).unwrap());
+    assert_open_started(client.open().unwrap());
     client.session.as_mut().unwrap().next_logical_seq = u64::MAX;
 
     assert!(matches!(
@@ -347,7 +347,7 @@ fn send_probe_reports_packets_sent_counter_overflow() {
         ..default_test_config(server.addr)
     };
     let mut client = Client::connect(config).unwrap();
-    assert_open_started(client.open(ClientTimestamp::now()).unwrap());
+    assert_open_started(client.open().unwrap());
     client.session.as_mut().unwrap().packets_sent = u64::MAX;
 
     assert!(matches!(
@@ -371,7 +371,7 @@ fn recv_once_returns_empty_on_timeout() {
         ..default_test_config(server.addr)
     };
     let mut client = Client::connect(config).unwrap();
-    assert_open_started(client.open(ClientTimestamp::now()).unwrap());
+    assert_open_started(client.open().unwrap());
     let events = client.recv_once().unwrap();
     assert!(events.is_empty());
     server.join();
@@ -477,7 +477,7 @@ fn recv_once_decodes_only_received_bytes_after_longer_datagram() {
         ..default_test_config(server.addr)
     };
     let mut client = Client::connect(config).unwrap();
-    assert_open_started(client.open(ClientTimestamp::now()).unwrap());
+    assert_open_started(client.open().unwrap());
 
     client.send_probe().unwrap();
     client.send_probe().unwrap();
@@ -550,7 +550,7 @@ fn echo_reply_metadata_propagates_observed_dscp_with_ancillary() {
         ..default_test_config(server.addr)
     };
     let mut client = Client::connect(config).unwrap();
-    assert_open_started(client.open(ClientTimestamp::now()).unwrap());
+    assert_open_started(client.open().unwrap());
 
     client.send_probe().unwrap();
     thread::sleep(Duration::from_millis(50));
@@ -757,7 +757,7 @@ fn wrong_token_reply_is_dropped() {
         ..default_test_config(server.addr)
     };
     let mut client = Client::connect(config).unwrap();
-    assert_open_started(client.open(ClientTimestamp::now()).unwrap());
+    assert_open_started(client.open().unwrap());
     client.send_probe().unwrap();
     thread::sleep(Duration::from_millis(30));
     let events = client.recv_once().unwrap();
@@ -796,7 +796,7 @@ fn duplicate_reply_emits_duplicate_event() {
         ..default_test_config(server.addr)
     };
     let mut client = Client::connect(config).unwrap();
-    assert_open_started(client.open(ClientTimestamp::now()).unwrap());
+    assert_open_started(client.open().unwrap());
     client.send_probe().unwrap();
     thread::sleep(Duration::from_millis(50));
 
@@ -850,7 +850,7 @@ fn out_of_order_reply_emits_late_event() {
         ..default_test_config(server.addr)
     };
     let mut client = Client::connect(config).unwrap();
-    assert_open_started(client.open(ClientTimestamp::now()).unwrap());
+    assert_open_started(client.open().unwrap());
     client.send_probe().unwrap();
     client.send_probe().unwrap();
     thread::sleep(Duration::from_millis(50));
@@ -891,7 +891,7 @@ fn poll_timeouts_emits_echo_loss() {
         ..default_test_config(server.addr)
     };
     let mut client = Client::connect(config).unwrap();
-    assert_open_started(client.open(ClientTimestamp::now()).unwrap());
+    assert_open_started(client.open().unwrap());
 
     client.send_probe().unwrap();
     client.send_probe().unwrap();
@@ -921,7 +921,7 @@ fn poll_timeouts_removes_expired_pending() {
         ..default_test_config(server.addr)
     };
     let mut client = Client::connect(config).unwrap();
-    assert_open_started(client.open(ClientTimestamp::now()).unwrap());
+    assert_open_started(client.open().unwrap());
 
     client.send_probe().unwrap();
     thread::sleep(Duration::from_millis(150));
@@ -967,7 +967,7 @@ fn late_reply_after_timeout_preserves_measurement_metadata() {
         ..default_test_config(server.addr)
     };
     let mut client = Client::connect(config).unwrap();
-    assert_open_started(client.open(ClientTimestamp::now()).unwrap());
+    assert_open_started(client.open().unwrap());
 
     client.send_probe().unwrap();
     thread::sleep(Duration::from_millis(60));
@@ -1046,7 +1046,7 @@ fn late_reply_metadata_is_unavailable_without_ancillary() {
         ..default_test_config(server.addr)
     };
     let mut client = Client::connect(config).unwrap();
-    assert_open_started(client.open(ClientTimestamp::now()).unwrap());
+    assert_open_started(client.open().unwrap());
 
     client.send_probe().unwrap();
     thread::sleep(Duration::from_millis(60));
@@ -1095,7 +1095,7 @@ fn late_reply_metadata_propagates_observed_dscp_with_ancillary() {
         ..default_test_config(server.addr)
     };
     let mut client = Client::connect(config).unwrap();
-    assert_open_started(client.open(ClientTimestamp::now()).unwrap());
+    assert_open_started(client.open().unwrap());
 
     client.send_probe().unwrap();
     thread::sleep(Duration::from_millis(60));
@@ -1149,7 +1149,7 @@ fn pending_map_bounded() {
         ..default_test_config(server.addr)
     };
     let mut client = Client::connect(config).unwrap();
-    assert_open_started(client.open(ClientTimestamp::now()).unwrap());
+    assert_open_started(client.open().unwrap());
     client.send_probe().unwrap();
     client.send_probe().unwrap();
     client.send_probe().unwrap();
@@ -1199,7 +1199,7 @@ fn minimal_negotiated_layout_works() {
         ..default_test_config(server.addr)
     };
     let mut client = Client::connect(config).unwrap();
-    assert_open_started(client.open(ClientTimestamp::now()).unwrap());
+    assert_open_started(client.open().unwrap());
     client.send_probe().unwrap();
     thread::sleep(Duration::from_millis(30));
     let events = client.recv_once().unwrap();
@@ -1253,7 +1253,7 @@ fn late_reply_with_pending_preserves_rtt() {
         ..default_test_config(server.addr)
     };
     let mut client = Client::connect(config).unwrap();
-    assert_open_started(client.open(ClientTimestamp::now()).unwrap());
+    assert_open_started(client.open().unwrap());
     client.send_probe().unwrap();
     client.send_probe().unwrap();
     client.send_probe().unwrap();
@@ -1296,7 +1296,7 @@ fn pending_full_does_not_send_packet() {
         ..default_test_config(server.addr)
     };
     let mut client = Client::connect(config).unwrap();
-    assert_open_started(client.open(ClientTimestamp::now()).unwrap());
+    assert_open_started(client.open().unwrap());
 
     client.send_probe().unwrap();
     client.send_probe().unwrap();
@@ -1361,7 +1361,7 @@ fn unmatched_future_reply_emits_warning_not_late() {
         ..default_test_config(server.addr)
     };
     let mut client = Client::connect(config).unwrap();
-    assert_open_started(client.open(ClientTimestamp::now()).unwrap());
+    assert_open_started(client.open().unwrap());
     client.send_probe().unwrap();
     thread::sleep(Duration::from_millis(50));
 
@@ -1419,7 +1419,7 @@ fn unmatched_future_reply_does_not_update_highest_received_seq() {
         ..default_test_config(server.addr)
     };
     let mut client = Client::connect(config).unwrap();
-    assert_open_started(client.open(ClientTimestamp::now()).unwrap());
+    assert_open_started(client.open().unwrap());
     client.send_probe().unwrap();
     client.send_probe().unwrap();
     thread::sleep(Duration::from_millis(50));
@@ -1523,7 +1523,7 @@ fn matched_reply_with_reversed_monotonic_time_still_emits_event() {
         ..default_test_config(server.addr)
     };
     let mut client = Client::connect(config).unwrap();
-    assert_open_started(client.open(ClientTimestamp::now()).unwrap());
+    assert_open_started(client.open().unwrap());
 
     let base = Instant::now() + Duration::from_secs(1);
     let send_ts = ClientTimestamp {
@@ -1566,7 +1566,7 @@ fn process_received_packet_uses_supplied_receive_metadata() {
         ..default_test_config(server.addr)
     };
     let mut client = Client::connect(config).unwrap();
-    assert_open_started(client.open(ClientTimestamp::now()).unwrap());
+    assert_open_started(client.open().unwrap());
 
     client.send_probe_at(ClientTimestamp::now()).unwrap();
     let recv_ts = ClientTimestamp::now();
@@ -1613,7 +1613,7 @@ fn process_received_packet_uses_supplied_receive_metadata_for_late_reply() {
         ..default_test_config(server.addr)
     };
     let mut client = Client::connect(config).unwrap();
-    assert_open_started(client.open(ClientTimestamp::now()).unwrap());
+    assert_open_started(client.open().unwrap());
 
     client.send_probe_at(ClientTimestamp::now()).unwrap();
     thread::sleep(Duration::from_millis(60));
@@ -1663,7 +1663,7 @@ fn receive_metadata_does_not_broaden_malformed_warning() {
         ..default_test_config(server.addr)
     };
     let mut client = Client::connect(config).unwrap();
-    assert_open_started(client.open(ClientTimestamp::now()).unwrap());
+    assert_open_started(client.open().unwrap());
 
     let events = client
         .process_received_packet(
@@ -1754,7 +1754,7 @@ fn send_probe_wraps_wire_sequence_at_u32_max() {
         ..default_test_config(server.addr)
     };
     let mut client = Client::connect(config).unwrap();
-    assert_open_started(client.open(ClientTimestamp::now()).unwrap());
+    assert_open_started(client.open().unwrap());
 
     let session = client.session.as_mut().unwrap();
     session.next_wire_seq = u32::MAX;
@@ -1811,7 +1811,7 @@ fn wrapped_reply_after_u32_max_is_not_late() {
         ..default_test_config(server.addr)
     };
     let mut client = Client::connect(config).unwrap();
-    assert_open_started(client.open(ClientTimestamp::now()).unwrap());
+    assert_open_started(client.open().unwrap());
     let session = client.session.as_mut().unwrap();
     session.next_wire_seq = u32::MAX;
     session.next_logical_seq = 41;
@@ -1848,7 +1848,7 @@ fn send_probe_after_sending_done_is_noop() {
         ..default_test_config(server.addr)
     };
     let mut client = Client::connect(config).unwrap();
-    assert_open_started(client.open(ClientTimestamp::now()).unwrap());
+    assert_open_started(client.open().unwrap());
 
     client.session.as_mut().unwrap().sending_done = true;
     let events = client.send_probe().unwrap();
@@ -1926,7 +1926,7 @@ fn recv_buffer_uses_negotiated_packet_length() {
         ..default_test_config(server.addr)
     };
     let mut client = Client::connect(config).unwrap();
-    assert_open_started(client.open(ClientTimestamp::now()).unwrap());
+    assert_open_started(client.open().unwrap());
     let buf_size = client.recv_buffer_size();
     assert!(
         buf_size > 4096,
@@ -1954,7 +1954,7 @@ fn short_echo_reply_does_not_emit_echo_reply() {
         ..default_test_config(server.addr)
     };
     let mut client = Client::connect(config).unwrap();
-    assert_open_started(client.open(ClientTimestamp::now()).unwrap());
+    assert_open_started(client.open().unwrap());
     client.send_probe().unwrap();
 
     let mut packet = echo_reply_packet(TOKEN, 0, &params, &TimestampFields::default(), None);
@@ -1986,7 +1986,7 @@ fn overlong_echo_reply_does_not_emit_echo_reply() {
         ..default_test_config(server.addr)
     };
     let mut client = Client::connect(config).unwrap();
-    assert_open_started(client.open(ClientTimestamp::now()).unwrap());
+    assert_open_started(client.open().unwrap());
     client.send_probe().unwrap();
 
     let mut packet = echo_reply_packet(TOKEN, 0, &params, &TimestampFields::default(), None);
@@ -2036,7 +2036,7 @@ fn overlong_datagram_detection_uses_extra_receive_byte() {
         ..default_test_config(server.addr)
     };
     let mut client = Client::connect(config).unwrap();
-    assert_open_started(client.open(ClientTimestamp::now()).unwrap());
+    assert_open_started(client.open().unwrap());
     assert_eq!(
         client.recv_buffer.len(),
         echo_packet_len(false, &params) + 1
@@ -2083,7 +2083,7 @@ fn exact_length_echo_reply_still_emits_echo_reply() {
         ..default_test_config(server.addr)
     };
     let mut client = Client::connect(config).unwrap();
-    assert_open_started(client.open(ClientTimestamp::now()).unwrap());
+    assert_open_started(client.open().unwrap());
     client.send_probe().unwrap();
 
     let events = client.recv_once().unwrap();
diff --git a/crates/irtt-client/src/client/tests/support.rs b/crates/irtt-client/src/client/tests/support.rs
index 59c7bcd..27a8f60 100644
--- a/crates/irtt-client/src/client/tests/support.rs
+++ b/crates/irtt-client/src/client/tests/support.rs
@@ -283,7 +283,7 @@ pub(super) fn open_client_with_echo_server(params: &Params) -> (Client, FakeServ
         ..default_test_config(server.addr)
     };
     let mut client = Client::connect(config).unwrap();
-    assert_open_started(client.open(ClientTimestamp::now()).unwrap());
+    assert_open_started(client.open().unwrap());
     (client, server)
 }
 
diff --git a/crates/irtt-client/src/client/tests/ttl.rs b/crates/irtt-client/src/client/tests/ttl.rs
index f1b30c8..acb4652 100644
--- a/crates/irtt-client/src/client/tests/ttl.rs
+++ b/crates/irtt-client/src/client/tests/ttl.rs
@@ -29,7 +29,7 @@ fn connect_applies_configured_ipv4_ttl_before_open_and_close_preserves_it() {
 
     assert_eq!(socket_ttl(&client.socket, client.remote).unwrap(), 64);
 
-    client.open(ClientTimestamp::now()).unwrap();
+    client.open().unwrap();
     server.join();
 
     client.close(ClientTimestamp::now()).unwrap();
diff --git a/crates/irtt-client/src/managed/runner.rs b/crates/irtt-client/src/managed/runner.rs
index 8daf702..ceb8202 100644
--- a/crates/irtt-client/src/managed/runner.rs
+++ b/crates/irtt-client/src/managed/runner.rs
@@ -94,7 +94,7 @@ impl ManagedClient {
             .transpose()?;
 
         let mut client = Client::connect(config)?;
-        let outcome = client.open(ClientTimestamp::now())?;
+        let outcome = client.open()?;
         publish_open_outcome(&hub, &outcome);
 
         let cancellation = CancellationToken::new();
diff --git a/crates/irtt-client/tests/hmac.rs b/crates/irtt-client/tests/hmac.rs
index d9c13a5..6edbe79 100644
--- a/crates/irtt-client/tests/hmac.rs
+++ b/crates/irtt-client/tests/hmac.rs
@@ -98,7 +98,7 @@ fn hmac_close_success_sends_authenticated_close_and_closes_session() {
     config.hmac_key = Some(key);
 
     let mut client = Client::connect(config).unwrap();
-    let outcome = client.open(ClientTimestamp::now()).unwrap();
+    let outcome = client.open().unwrap();
     assert_started(outcome, &params);
 
     let events = client.close(ClientTimestamp::now()).unwrap();
@@ -132,7 +132,7 @@ fn missing_client_key_against_hmac_required_server_times_out() {
 
     let mut client = Client::connect(config).unwrap();
     assert!(matches!(
-        client.open(ClientTimestamp::now()),
+        client.open(),
         Err(ClientError::OpenTimeout)
     ));
 
@@ -157,7 +157,7 @@ fn wrong_client_key_against_hmac_required_server_times_out() {
 
     let mut client = Client::connect(config).unwrap();
     assert!(matches!(
-        client.open(ClientTimestamp::now()),
+        client.open(),
         Err(ClientError::OpenTimeout)
     ));
 
@@ -185,7 +185,7 @@ fn bad_hmac_echo_reply_is_rejected_without_echo_reply_event() {
     };
 
     let mut client = Client::connect(config).unwrap();
-    let outcome = client.open(ClientTimestamp::now()).unwrap();
+    let outcome = client.open().unwrap();
     assert_started(outcome, &params);
 
     let sent = client.send_probe().unwrap();
@@ -229,7 +229,7 @@ fn hmac_open_reply_with_bad_hmac_fails_with_protocol_error() {
 
     let mut client = Client::connect(config).unwrap();
     assert!(matches!(
-        client.open(ClientTimestamp::now()),
+        client.open(),
         Err(ClientError::Protocol(ProtoError::BadHmac))
     ));
     server.join();
@@ -247,7 +247,7 @@ fn non_hmac_client_open_does_not_set_hmac_flag() {
     config.hmac_key = None;
 
     let mut client = Client::connect(config).unwrap();
-    let outcome = client.open(ClientTimestamp::now()).unwrap();
+    let outcome = client.open().unwrap();
     assert_started(outcome, &params);
 
     let observations = server.observations(1);
@@ -304,7 +304,7 @@ fn backend_hmac_correct_key_succeeds() {
     config.hmac_key = Some(key);
 
     let mut client = Client::connect(config).unwrap();
-    let outcome = client.open(ClientTimestamp::now()).unwrap();
+    let outcome = client.open().unwrap();
     assert!(matches!(outcome, OpenOutcome::Started { .. }));
 
     let sent = client.send_probe().unwrap();
@@ -327,7 +327,7 @@ fn backend_hmac_wrong_key_fails() {
 
     let mut client = Client::connect(config).unwrap();
     assert!(matches!(
-        client.open(ClientTimestamp::now()),
+        client.open(),
         Err(ClientError::OpenTimeout)
     ));
 }
@@ -342,7 +342,7 @@ fn backend_hmac_missing_key_fails() {
 
     let mut client = Client::connect(config).unwrap();
     assert!(matches!(
-        client.open(ClientTimestamp::now()),
+        client.open(),
         Err(ClientError::OpenTimeout)
     ));
 }
diff --git a/crates/irtt-client/tests/large_packets.rs b/crates/irtt-client/tests/large_packets.rs
index d3cc650..39f8d1f 100644
--- a/crates/irtt-client/tests/large_packets.rs
+++ b/crates/irtt-client/tests/large_packets.rs
@@ -128,7 +128,7 @@ fn backend_large_packet_smoke() {
     })
     .unwrap();
 
-    let outcome = client.open(ClientTimestamp::now()).unwrap();
+    let outcome = client.open().unwrap();
     assert!(matches!(outcome, irtt_client::OpenOutcome::Started { .. }));
 
     client.send_probe().unwrap();
diff --git a/crates/irtt-client/tests/protocol_options.rs b/crates/irtt-client/tests/protocol_options.rs
index 34cbb60..44bac90 100644
--- a/crates/irtt-client/tests/protocol_options.rs
+++ b/crates/irtt-client/tests/protocol_options.rs
@@ -167,7 +167,7 @@ fn strict_open_rejects_changed_compatibility_params_from_server() {
         config.server_addr = server.addr.to_string();
         let mut client = Client::connect(config).unwrap();
         assert!(matches!(
-            client.open(irtt_client::ClientTimestamp::now()),
+            client.open(),
             Err(ClientError::NegotiationRejected { .. })
         ));
         server.join();
@@ -379,7 +379,7 @@ fn backend_basic_open_echo_close() {
     let peer = BackendPeer::start_open_echo(params.clone(), None);
     let mut client = Client::connect(config_for_params(peer.addr(), &params)).unwrap();
 
-    let outcome = client.open(ClientTimestamp::now()).unwrap();
+    let outcome = client.open().unwrap();
     assert!(matches!(outcome, irtt_client::OpenOutcome::Started { .. }));
 
     let sent = client.send_probe().unwrap();
@@ -400,7 +400,7 @@ fn backend_ttl_smoke() {
     config.socket_config.ttl = Some(64);
     let mut client = Client::connect(config).unwrap();
 
-    let outcome = client.open(ClientTimestamp::now()).unwrap();
+    let outcome = client.open().unwrap();
     assert!(matches!(outcome, irtt_client::OpenOutcome::Started { .. }));
 
     let sent = client.send_probe().unwrap();
@@ -420,7 +420,7 @@ fn dscp_configured_open_close_smoke() {
     let server = start_open_server(params.clone(), None);
     let mut client = Client::connect(config_for_params(server.addr, &params)).unwrap();
 
-    let outcome = client.open(ClientTimestamp::now()).unwrap();
+    let outcome = client.open().unwrap();
     assert!(matches!(outcome, irtt_client::OpenOutcome::Started { .. }));
     client.close(ClientTimestamp::now()).unwrap();
     server.join();
@@ -438,7 +438,7 @@ fn backend_received_stats_smoke() {
         let peer = BackendPeer::start_open_echo(params.clone(), None);
         let mut client = Client::connect(config_for_params(peer.addr(), &params)).unwrap();
 
-        client.open(ClientTimestamp::now()).unwrap();
+        client.open().unwrap();
         client.send_probe().unwrap();
         let events = client.recv_once().unwrap();
         assert_eq!(events.len(), 1);
@@ -461,7 +461,7 @@ fn backend_timestamp_smoke() {
         let peer = BackendPeer::start_open_echo(params.clone(), None);
         let mut client = Client::connect(config_for_params(peer.addr(), &params)).unwrap();
 
-        client.open(ClientTimestamp::now()).unwrap();
+        client.open().unwrap();
         client.send_probe().unwrap();
         let events = client.recv_once().unwrap();
         assert_eq!(events.len(), 1);
@@ -508,7 +508,7 @@ fn backend_clock_smoke() {
         let peer = BackendPeer::start_open_echo(params.clone(), None);
         let mut client = Client::connect(config_for_params(peer.addr(), &params)).unwrap();
 
-        client.open(ClientTimestamp::now()).unwrap();
+        client.open().unwrap();
         client.send_probe().unwrap();
         let events = client.recv_once().unwrap();
         assert_eq!(events.len(), 1);
diff --git a/crates/irtt-client/tests/server_fill.rs b/crates/irtt-client/tests/server_fill.rs
index 7a453fa..af9c1c3 100644
--- a/crates/irtt-client/tests/server_fill.rs
+++ b/crates/irtt-client/tests/server_fill.rs
@@ -112,7 +112,7 @@ fn server_fill_strict_rejects_removed_fill() {
     let server = start_open_server(returned, None);
     let mut client = Client::connect(config_for_params(server.addr, &requested)).unwrap();
     assert!(matches!(
-        client.open(ClientTimestamp::now()),
+        client.open(),
         Err(ClientError::NegotiationRejected { .. })
     ));
     server.join();
@@ -129,7 +129,7 @@ fn server_fill_strict_rejects_different_fill_value() {
     let server = start_open_server(returned, None);
     let mut client = Client::connect(config_for_params(server.addr, &requested)).unwrap();
     assert!(matches!(
-        client.open(ClientTimestamp::now()),
+        client.open(),
         Err(ClientError::NegotiationRejected { .. })
     ));
     server.join();
@@ -145,7 +145,7 @@ fn server_fill_strict_rejects_unexpected_fill_from_server() {
     let server = start_open_server(returned, None);
     let mut client = Client::connect(config_for_params(server.addr, &requested)).unwrap();
     assert!(matches!(
-        client.open(ClientTimestamp::now()),
+        client.open(),
         Err(ClientError::NegotiationRejected { .. })
     ));
     server.join();
diff --git a/crates/irtt-client/tests/support/mod.rs b/crates/irtt-client/tests/support/mod.rs
index fb49e35..02dec96 100644
--- a/crates/irtt-client/tests/support/mod.rs
+++ b/crates/irtt-client/tests/support/mod.rs
@@ -216,7 +216,7 @@ where
 {
     let server = start_one_probe_server(server_params, timestamps, hmac_key);
     let mut client = Client::connect(build_config(server.addr)).unwrap();
-    let negotiated = assert_started(client.open(ClientTimestamp::now()).unwrap());
+    let negotiated = assert_started(client.open().unwrap());
 
     let sent_events = client.send_probe().unwrap();
     assert_eq!(sent_events.len(), 1);