diff --git a/packages/mosaic/framework/tools/wake/test-wake-store-ack.sh b/packages/mosaic/framework/tools/wake/test-wake-store-ack.sh
index eceecc7e..a26f233c 100755
--- a/packages/mosaic/framework/tools/wake/test-wake-store-ack.sh
+++ b/packages/mosaic/framework/tools/wake/test-wake-store-ack.sh
@@ -247,11 +247,19 @@ EOF
   done
   # Background sync deliberately SLOW: proves the ack does not wait for it.
   export WAKE_ACK_SYNC_CMD="sleep 3; touch '$WAKE_STATE_HOME/SYNC_DONE'"
-  start="$(date +%s)"
+  # Sub-second timing (#918): `date +%s` is SECOND-granularity, so a
+  # legitimately fast (sub-second) ack that straddles a wall-clock second
+  # boundary can misreport elapsed=2s and flake under CI load (observed on
+  # Woodpecker pipeline 2057; 20/20 passes locally elsewhere). Use
+  # `date +%s.%N` and compare in milliseconds via awk (bash `[ ]` can't do
+  # float/ms math) against a threshold comfortably below the 3s background
+  # sync — proving the ack did NOT wait on it — while tolerating a
+  # legitimate sub-second-to-~1s ack across a boundary.
+  start="$(date +%s.%N)"
   out="$(PATH="$bin:$PATH" "$ACK" consumed --upto 1 --wake-id WID-1)"
-  end="$(date +%s)"
-  elapsed=$((end - start))
-  [ "$elapsed" -lt 2 ] || fail_msg "T7: ack path blocked ${elapsed}s — must return without waiting on the background sync"
+  end="$(date +%s.%N)"
+  elapsed_ms="$(awk -v s="$start" -v e="$end" 'BEGIN { printf "%d", (e - s) * 1000 }')"
+  [ "$elapsed_ms" -lt 1500 ] || fail_msg "T7: ack path blocked ${elapsed_ms}ms — must return without waiting on the background sync"
   echo "$out" | grep -q 'CONSUMED 1' || fail_msg "T7: CONSUMED not reported [$out]"
   # Local write is durable IMMEDIATELY (no network needed to record the ack).
   STATE_DIR="$WAKE_STATE_HOME/default"