When creating new VM you can set System Clock to Local or UTC.
But its important to choose according to what is your VM system.
Linux needs UTC and Windows needs Local, otherwise they may not work correctly.
For example if you use Local for Debian, it breaks. EDIT: VMs Losing DHCP Lease on TrueNAS Core 13.0 - Network Issue or Time Sync Issue?
On the other hand Windows expects Local.
So I propose to include short description to each setting like this:
System Clock:
Local (for Windows guests)
UTC (for Linux guests)