setup: pick host-dependent start time

initial-setup.sh

@@ -222,14 +222,20 @@ configure_systemd()
 
     log "Creating systemd files"
 
+    # Choose a time between 1am and 6am based on this hostname
+    HASH=$(echo hash of "$HOSTNAME" | sha1sum)
+    HOUR=$((0x${HASH:0:8} % 5 + 1))
+    MINUTE=$((0x${HASH:8:8} % 6 * 10))
+    TIME=$(printf %02d:%02d:00 $HOUR $MINUTE)
+
+    log "Backup time is $TIME"
+
     cat > "$TIMER_UNIT" <<EOF
 [Unit]
 Description=Borg backup to ${BACKUP_HOST}
 
 [Timer]
-OnCalendar=*-*-* 01:00:00
-RandomizedDelaySec=1800
-FixedRandomDelay=true
+OnCalendar=*-*-* $TIME
 Persistent=true
 
 [Install]