Maybe your BIOS battery is going bad? It's the battery on your motherboard that looks like a watch battery. Round and flat and about the size of a quarter. Just shutdown the machine, pop it out and replace it. Cheap and easy to fix, assuming thats' your problem.
You can also run a time sync from your cron.daily.
rdate somehost.domain.com
Replace "host.domain.com" with one of the "hostnames" from this list...
http://ntp.isc.org/bin/view/Servers/...TwoTimeServers