systemd-timesyncd.service isn't enough, for various reasons:
- it is started too early in the boot process - files in
/var/run/qubes-services are not yet there
- by default it does only one shot synchronization, and there is no
network at that early boot time yet
- by default use-ntp is set to "no"
So, in addition, enable actual ntp client.
FixesQubesOS/qubes-issues#3210
Files in /var/run/qubes-service are created by qubes-sysinit.service. So
defer that condition check after that service start.
Thanks @adrelanos for the report.
FixesQubesOS/qubes-issues#1985