Hah interesting. Is it on time every time, or usually, or sporadically?
Can you think of anything that changed on the computer recently, or are you digging it out of a closet, or what?
What browser are you using? Have you tried using a different browser version?
What about the windows profile, have you tried creating a new account and logging in to see if that behaves any differently?
Sounds like a pain..report back with some of that and maybe we'll get to the bottom.