I have experienced something strange on Hyper V cluster based on Windows Server 2008 R2 SP1 Enterprise and VM guest with same OS but Standard edition, with time synchronization enabled but VM was still out of sync.
I have checked that Windows time service was running and queried the source for synchronization and it was free running system clock !
After restarting the windows time service, the VM started to sync with local CMOS clock instead of synchronizing with host (parent partition).
I'm guessing that VM was not reading the setting for the time synchronization from the VM configuration, so I have disabled the setting and re enabled and restarted the windows time service, and finally within few seconds the VM was synchronizing the time with host :
One more thing : if the server is Windows 2008 R2 and the machine is not domain joined the windows time service will stop automatically. On reboot you can see the following event :
This behaviour is by default and you can find more info on translated Japanese kb :
http://translate.google.com/translate?hl=en&sl=ja&u=http://support.microsoft.com/kb/2385818/ja
