diff --git a/deploy/wizwar-backup.sh b/deploy/wizwar-backup.sh
index 2f15b8c..d9abc41 100755
--- a/deploy/wizwar-backup.sh
+++ b/deploy/wizwar-backup.sh
@@ -11,7 +11,12 @@ STAMP=$(date +%Y-%m-%d)
 # Sentry Crons check-in: /root/.wizwar-sentry-cron holds the check-in URL
 # (auto-creates the monitor on first ping). Absent file = no check-ins.
 CRON_URL=$(cat /root/.wizwar-sentry-cron 2>/dev/null || true)
-checkin() { [ -n "$CRON_URL" ] && curl -sf -o /dev/null "$CRON_URL?status=$1" || true; }
+# One check-in, when the run ends, carrying its duration: a start and a
+# finish sent seconds apart can reach Sentry in either order, and a start
+# that lands second is never closed. A run that never ends sends nothing,
+# and Sentry marks the night missed.
+START=$SECONDS
+checkin() { [ -n "$CRON_URL" ] && curl -sf -o /dev/null "$CRON_URL?status=$1&duration=$((SECONDS - START))" || true; }
 
 if grep -q CHANGE_ME /root/.config/rclone/rclone.conf; then
   echo "$(date -Is) skipped: Spaces credentials not configured yet" >> "$LOG"
@@ -20,7 +25,6 @@ fi
 
 {
   echo "=== $(date -Is) backup start"
-  checkin in_progress
   if rclone sync "$SRC" "spaces:$BUCKET/wizwar/current" 2>&1 &&
      rclone copy "$SRC" "spaces:$BUCKET/wizwar/snapshots/$STAMP" 2>&1; then
     checkin ok
diff --git a/deploy/wizwar-rollup.sh b/deploy/wizwar-rollup.sh
index b06bcfc..737a53c 100755
--- a/deploy/wizwar-rollup.sh
+++ b/deploy/wizwar-rollup.sh
@@ -21,13 +21,17 @@ CRON_URL=$(cat /root/.wizwar-sentry-cron-rollup 2>/dev/null || true)
 # The check-in carries the schedule: Sentry only keeps a monitor it has
 # been told the shape of, and a bare ping to an unknown slug is accepted
 # and dropped without a word.
+# One check-in, when the run ends, carrying its duration: a start and a
+# finish sent seconds apart can reach Sentry in either order, and a start
+# that lands second is never closed. A run that never ends sends nothing,
+# and Sentry marks the night missed.
+START=$SECONDS
 checkin() {
   [ -n "$CRON_URL" ] && curl -sf -o /dev/null -X POST -H "Content-Type: application/json" \
-    -d "{\"status\":\"$1\",\"monitor_config\":{\"schedule\":{\"type\":\"crontab\",\"value\":\"$SCHEDULE\"},\"checkin_margin\":30,\"max_runtime\":10,\"timezone\":\"UTC\"}}" \
+    -d "{\"status\":\"$1\",\"duration\":$((SECONDS - START)),\"monitor_config\":{\"schedule\":{\"type\":\"crontab\",\"value\":\"$SCHEDULE\"},\"checkin_margin\":30,\"max_runtime\":10,\"timezone\":\"UTC\"}}" \
     "$CRON_URL" || true
 }
 
-checkin in_progress
 if python3 - "$DAY" "$OUT" <<'PY' >> "$LOG" 2>&1
 import json, sys, os, glob, gzip, datetime, collections, subprocess, re
 day, out = sys.argv[1], sys.argv[2]