I've been having a really odd problem lately where my computer clock can lose as much as 4 - 5 minutes per hour. I've had batteries die on the Motherboard, and clock became wrong, but never had it run slow. Anyway, I replaced the Battery and no help.
I think I've resolved the problem by getting rid of Mcafee Viruscan 5.x after reading some related threads somewhere on this 'Lost Time' thing. Others reported similar situations where the clock can lose time while computer is on but corrects itself after a shutdown or reboot. I didn't notice if it corrected itself on my machine, but it may have. Other symptoms were a jerky mouse and 'delayed action' on many things. Strange stuff!
Much better now, except I can't get Mcafee Viruscan 6.x to install correctly with it's automated Update Feature.