You need root privileges (sudo hwclock).
Works in dom0 and sys-net.
You didn’t mention if you have search on the forum:
https://forum.qubes-os.org/search?q=time
https://forum.qubes-os.org/search?q=time%20sync
Maybe these related topics will help you:
https://forum.qubes-os.org/t/qubes-users-problems-with-timesynchronization/12730
https://forum.qubes-os.org/t/definitive-guide-to-time-setting-sync-in-qubes-os/17641