I’m using 11.4 in a multiboot setup with Windows 7 and 11.3 (I installed 11.4 in its own partition and then added it to GRUB in 11.3).
I wanted to try systemd so added it to 11.4.
If I boot with systemV init then ntp starts and sets time correctly.
If I boot with systemd then it all starts fine but the clock is an hour slow but still claims to be in BST. If I go into settings and set locale without changing value it corrects the time.
(Because of Windows the system clock is set to local time).
There are timing errors between Win and Linux and there’s a timezone fix from Win 7 that I don’t have the link for at the moment. It updates the timezones.
Starting out I’d set other system clocks (including the BIOS) to the same timezones, UTC and DST as OS 11.3. Use the same NTP Internet time providers as 11.3. Because you have 3 systems on the same machine I don’t think its a BIOS clock issue (HW clock) even though systems update the HW clock when rebooting.