Access restricted by time?

Here's a general question that I've been puzzling over.

Using either a 2600 router (on a stick) or a 2950 switch, is there a way to
stop one specific computer from getting to the internet? If there is, can
anyone point me in the right direction? I've been racking my brains but I
keep drawing a blank.

Here's the whole picture.

2600 router on a stick
All machines connceted to a 2950
VLAN1 for administration (of course)
VLAN2 has 3 machines
I want to be able to block internet access for 1 machine on VLAN2 after
11PM, but allow the other 2 machines to access the internet. Of course then
I'll need to turn it back on, probably about 6AM.

Any help is greatly appreciated and thanks for picking your brains.