I use a CentOS5.8 server with KVM. I have several virtual machines running on it. When I reboot the server (takes 10 minutes) all VMs are saved and correctly restored. The time on the clients is however of by 10 minutes. nptd is running on the clie..
There was a recent forum thread  on this issue. Unfortunately it was never cleanly resolved, but you may find some suggestions there. It seems that unmatched memory modules may be a cause.https://www.centos.org/modules/newbb/viewtopic.php?topic_id=35167&forum=55&post_id=151503#forumpost1515..