The qubes-sync-time needs qrexec running to work, so set start order appropriately.
@@ -1,7 +1,8 @@
[Unit]
Description=Update time from ClockVM
+After=qubes-qrexec-agent.service
ConditionPathExists=!/var/run/qubes-service/clocksync
[Service]
ExecStart=/usr/bin/qvm-sync-clock
-User=root
+User=root