diff --git a/docs/engineering/hil-test-matrix.md b/docs/engineering/hil-test-matrix.md
index 6deb04d..1ddb5e2 100644
--- a/docs/engineering/hil-test-matrix.md
+++ b/docs/engineering/hil-test-matrix.md
@@ -3,7 +3,7 @@
 | Area | Stimulus | Required evidence | Expected result |
 |---|---|---|---|
 | Boot | Flash/start both boards | `boot`, `role`, periodic `health` from each | Exactly one sender and receiver; no reset loop; bounded heap/stack |
-| Time | Sender receive window and receiver time-sync | sender request/completion, receiver transmit | Valid UTC completion; misses remain visible |
+| Time | Sender receive window and receiver startup time-sync burst | sender request/completion, receiver startup transmit | Valid UTC completion during the 180 s baseline; misses remain visible |
 | Meter baseline | Real optical meter | `meter_frame`, `meter_sample` | Frame classification and seconds index when present; no secrets/values logged |
 | Batch | Normal 30 s batching | create, encode, every TX/RX chunk, complete, decode, ACK TX/RX | One batch ID correlates end to end |
 | Meter timeout | Partial start then >1.5 s pause | `classification=timeout`, health | No reset; next valid fixture recovers |
diff --git a/src/main.cpp b/src/main.cpp
index cad592e..b78b2fe 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -34,6 +34,7 @@ static SenderStatus g_sender_statuses[NUM_SENDERS];
 static bool g_ap_mode = false;
 static WifiMqttConfig g_cfg;
 static uint32_t g_last_timesync_ms = 0;
+static uint32_t g_receiver_startup_timesync_last_ms = 0;
 static constexpr uint32_t TIME_SYNC_OFFSET_MS = 15000;
 static uint32_t g_boot_ms = 0;
 static FaultCounters g_sender_faults = {};
@@ -1338,6 +1339,14 @@ static void receiver_loop() {
   uint32_t now_ms = millis();
   if (!g_ap_mode) {
     bool burst_sent = false;
+    const char *burst_mode = "burst";
+    if (time_is_synced() && now_ms - g_boot_ms < TIME_SYNC_BURST_DURATION_MS &&
+        (g_receiver_startup_timesync_last_ms == 0 ||
+         now_ms - g_receiver_startup_timesync_last_ms >= TIME_SYNC_BURST_INTERVAL_MS)) {
+      g_receiver_startup_timesync_last_ms = now_ms;
+      burst_sent = true;
+      burst_mode = "startup";
+    }
     for (uint8_t i = 0; i < NUM_SENDERS; ++i) {
       TimeSyncBurstState &state = g_timesync_burst[i];
       if (state.active) {
@@ -1356,10 +1365,10 @@ static void receiver_loop() {
         display_set_last_error(g_receiver_last_error, g_receiver_last_error_utc, g_receiver_last_error_ms);
       }
       if (SERIAL_DEBUG_MODE) {
-        serial_debug_printf("timesync: tx burst");
+        serial_debug_printf("timesync: tx %s", burst_mode);
       }
-      hil_trace_eventf("time_bootstrap", "\"stage\":\"transmit\",\"mode\":\"burst\",\"ok\":%s,\"utc\":%lu",
-                       time_sent ? "true" : "false", static_cast<unsigned long>(time_get_utc()));
+      hil_trace_eventf("time_bootstrap", "\"stage\":\"transmit\",\"mode\":\"%s\",\"ok\":%s,\"utc\":%lu",
+                       burst_mode, time_sent ? "true" : "false", static_cast<unsigned long>(time_get_utc()));
       g_last_timesync_ms = now_ms;
     } else if (now_ms - g_last_timesync_ms > interval_sec * 1000UL) {
       g_last_timesync_ms = now_ms;