diff --git a/config/config.example.ini b/config/config.example.ini
index bae976f..c76489a 100644
--- a/config/config.example.ini
+++ b/config/config.example.ini
@@ -100,7 +100,8 @@ frame_timeout_ms = 5000
 
 ; --- A thermal camera (InfraTec TarisIR mini), beside the colour one ---------
 ; It takes its picture at the same waypoints and intervals, right after the
-; colour camera, and both carry the same timestamp: RGB/<t>.jxl and TIR/<t>.jxl.
+; colour camera. Each file and CamEvent has the time its own frame arrived; the
+; two of one waypoint share hdg/pit and are at most max_frame_age_ms apart.
 ; The counts are saved 16-bit and always lossless (jxl_distance must stay 0);
 ; T[K] = count x 0.01 under profile 0, x 0.02 under profile 1, emissivity 1.
 ; Its driver, id (the serial) and interface belong in hardware.ini; [Hardware]
diff --git a/docs/architecture.md b/docs/architecture.md
index fe95cea..5b8d451 100644
--- a/docs/architecture.md
+++ b/docs/architecture.md
@@ -140,8 +140,9 @@ With a thermal camera the scheduler and the pipeline still see one
 the one the keep rule reads) and the thermal one after them. Its `trigger()`
 asks the colour source first; only if that delivered does it ask the thermal
 source, which hands over its newest frame if it is no older than
-`max_frame_age_ms` and otherwise says no at once. Every frame of one trigger
-takes the colour frame's timestamp. The colour camera failing stops the run as
+`max_frame_age_ms` and otherwise says no at once. Each frame keeps the time it
+reached the host, so the two of one waypoint differ by up to that age. The
+colour camera failing stops the run as
 before; the thermal one failing never does (`offline()` says why, Health
 `cams_offline` names it). Thermal frames are `Mono16` counts: the pipeline
 rotates them, takes `tmax`/`tmed`/hot spot on the rotated image
diff --git a/docs/configuration.md b/docs/configuration.md
index 82cade6..1f85a1b 100644
--- a/docs/configuration.md
+++ b/docs/configuration.md
@@ -1065,9 +1065,9 @@ firmware `ST` lines (per-axis state + encoder counts), parsed by
 
 A TarisIR mini beside the colour camera takes its picture at the same waypoints
 and intervals: the colour camera is asked first, and only once it has delivered
-is the thermal one asked for its newest frame. Both frames carry the colour
-frame's timestamp, so `RGB/<t>.jxl` and `TIR/<t>.jxl` are a pair (and so are
-their CamEvents, see [mqtt-api.md](mqtt-api.md#thermal-camera-cam-tir)).
+is the thermal one asked for its newest frame. Each file and CamEvent has the
+time its own frame arrived: the two of one waypoint share `hdg`/`pit` and are at
+most `max_frame_age_ms` apart (see [mqtt-api.md](mqtt-api.md#thermal-camera-cam-tir)).
 
 - **Best effort.** A thermal camera that is missing, unlicensed or has no fresh
   frame costs that picture its thermal image, nothing more: the scan goes on, the
diff --git a/docs/mqtt-api.md b/docs/mqtt-api.md
index d47b0aa..598e080 100644
--- a/docs/mqtt-api.md
+++ b/docs/mqtt-api.md
@@ -153,9 +153,12 @@ their payload is unchanged.
 | `tmed` | int/null | Median of the image, tenths of a °C (the anchor for a display window) |
 | `hotx`, `hoty` | number/null | Where the hottest pixel is: its centre, 0..1 across and down the image **as stored** (after `rotation_deg`), as for detection boxes |
 
-- **Same `time` as the colour picture.** The thermal camera is asked right after
-  the colour one, at the same waypoint, and its event and file take the colour
-  frame's timestamp: `RGB/<time>.jxl` and `TIR/<time>.jxl` are one pair. A
+- **Its own `time`.** The thermal camera is asked right after the colour one, at
+  the same waypoint, and hands over the newest frame it has. `time` (and the file
+  name) is when that frame reached the tower computer, so it is up to
+  `max_frame_age_ms` (400) off the colour picture's, earlier or later. The `RGB`
+  and `TIR` event of one waypoint share `hdg` and `pit` (sampled together) and
+  follow each other in the stream; pair them by that, not by an equal `time`. A
   picture the thermal camera had no fresh frame for has no `TIR` event.
 - **The file holds counts**, 16-bit single channel, lossless:
   `T[K] = count × 0.01` under `cal` 0 (`FF (-40-120C)`), `× 0.02` under `cal` 1
diff --git a/include/fgc/CompositeCameraSource.h b/include/fgc/CompositeCameraSource.h
index 2972cbb..17436a0 100644
--- a/include/fgc/CompositeCameraSource.h
+++ b/include/fgc/CompositeCameraSource.h
@@ -19,8 +19,9 @@ namespace fgc {
 // frame for the same waypoint. The others are best effort - a follower with
 // no fresh frame costs that picture its thermal image, nothing more.
 //
-// Every frame of one trigger carries the leader's timestamp, so the pair is
-// RGB/<t>.jxl and TIR/<t>.jxl with the same <t> in both CamEvents.
+// Every frame keeps its own time, when it reached the host: the thermal frame
+// is the newest the camera had, so its time is up to max_frame_age_ms off the
+// colour one, and that is what the file name and the CamEvent say.
 //
 // A follower that is briefly without a fresh frame (frameReady() false: the
 // thermal camera's NUC) holds the picture back for up to `follower_wait_ms`,
@@ -71,8 +72,6 @@ private:
     std::vector<int> counts_;      // cameras each child is configured with
     std::vector<int> offsets_;     // global index of each child's camera 0
     FrameCallback    callback_;
-    bool             in_trigger_ = false;
-    long long        shot_ts_    = 0;   // the leader's frame time, during a trigger
     int              follower_wait_ms_;
     long long        waiting_since_ = 0;   // steady ms a picture began waiting for a follower
 };
diff --git a/src/camera/CompositeCameraSource.cpp b/src/camera/CompositeCameraSource.cpp
index 2953370..59103b0 100644
--- a/src/camera/CompositeCameraSource.cpp
+++ b/src/camera/CompositeCameraSource.cpp
@@ -76,12 +76,9 @@ bool CompositeCameraSource::trigger() {
                   << " ms; taking the picture without it";
     }
     waiting_since_ = 0;
-    in_trigger_ = true;
-    shot_ts_    = 0;
     const bool taken = children_[0]->trigger();
     if (taken)
         for (size_t k = 1; k < children_.size(); ++k) children_[k]->trigger();
-    in_trigger_ = false;
     return taken;
 }
 
@@ -100,7 +97,6 @@ void CompositeCameraSource::setFrameCallback(FrameCallback cb) {
     // The leader's frames pass through untouched (they can be 24 MB); its
     // camera 0 is global camera 0, so not even the index changes.
     children_[0]->setFrameCallback([this](const Frame& f) {
-        if (in_trigger_ && shot_ts_ == 0) shot_ts_ = f.timestamp_ms;
         if (callback_) callback_(f);
     });
     for (size_t k = 1; k < children_.size(); ++k) {
@@ -109,7 +105,6 @@ void CompositeCameraSource::setFrameCallback(FrameCallback cb) {
             if (!callback_) return;
             Frame g  = f;
             g.cam_id = f.cam_id + offset;
-            if (in_trigger_ && shot_ts_ != 0) g.timestamp_ms = shot_ts_;
             callback_(g);
         });
     }
diff --git a/tests/test_composite.cpp b/tests/test_composite.cpp
index be5c51b..65c7668 100644
--- a/tests/test_composite.cpp
+++ b/tests/test_composite.cpp
@@ -100,12 +100,12 @@ TEST_CASE("the composite numbers the cameras leader first, and counts them all")
     CHECK(r.frames[2].cam_id == 2);   // the thermal camera
 }
 
-TEST_CASE("one trigger gives every frame the leader's time") {
+TEST_CASE("every frame keeps the time it arrived, the follower's too") {
     Rig r;
     REQUIRE(r.src->trigger());
     REQUIRE(r.frames.size() == 2);
     CHECK(r.frames[0].timestamp_ms == 1000);
-    CHECK(r.frames[1].timestamp_ms == 1000);   // not its own 5000
+    CHECK(r.frames[1].timestamp_ms == 5000);   // its own, not the leader's
 }
 
 TEST_CASE("the followers are asked only once the leader has delivered") {