Time controlled network connection



I have a friend who works with me, alot in the afternoons and late nights.
And he found out that his kids sit up late on schooldays doing IRC, they are only 10-13 years old..so that worries him that he can not oversee who they talk to, and so, plus he wants them to take care of the schoolwork first of all.

He asked me if there is any way to to put like a "time control" on the network card.
He has a xDSL-connection, so he wish he can set something like a timer or so, so the card will be inactive between certain hours.

I have no idea..so I said I will ask around if there is any way to fix it.

So, I was hoping that someone here has a good idea on what can be done.
Anyhing that can be done in Windows XP, or is there any software out that can something in that way...??

Thanks! :)
You could also use a router/firewall. I have a D-Link DI601 and it gives me the ability to block ports during certain hours, filter out webpages with certain words on them, and much more. Good luck!