Looking into it, I think that there is a good chance it's just a windows thing.
Control panel -> Parental Controls -> Click on user -> Time limits
http://i146.photobucket.com/albums/r...g?t=1214280852
If he has a password, then sorry, you'll have to work harder.
If it is on the windows machine, you can change the BIOS clock, which will confuse Windows so long as it doesn't update the time via the internet.