I noticed UCS wasn’t syncing time. After investigation it was because of the existence of a file
/run/ntp.conf.dhcp. I set the dhcp option for ntp to provide the IP address of the DC to all other clients in this subnet. I expected UCS to ignore this setting if it was the DC and if timeservers are configured.
I could only solve this by removing the dhcp option, running
dhclienton the relevant interface, deleting the file mentioned above and
/run/ntpdate.dhcp, and restarting ntp:
systemctl restart ntp.service.