virtualbox.org

I noticed that when my host goes to hibernation, my running guest VMs' system clocks get out of sync. So I have to reset it every time in individual boxes, which is annoying. Any permanent fix for this?

Sure, the best fix is never to hibernate. Other than that, AFAICS, VBox can't control how often each guest OS reads the RTC.

Will using network time make a difference?

Depends how often the guest checks network time.

Sometimes people use their personal boxes to try out different OSs with VirtualBox. So putting your machine on hibernation cannot be avoided. This sounds like a good feature for VirtualBox to implement - detect when host machine has woke up and then resync all running guest VMs' clocks.