An unusual Instant Messenger question

[bill at billhorne.homelinux.org (Bill Horne)]

Thanks for reading this: I've got an unusual question about the 
AOL Instant Messenger service.

My son has just discovered IM, and is prone to chat for hours 
on end instead of doing homework. I've put controls on the IM 
port numbers in iptables, tripped by a cron job that limits his 
logon time. So far, so good: no problem.

But, when the cron job runs, his IM sessions stall, and the kids 
he's been online with all pick up the phone and ask him what's 
wrong. I'd like to automate an IM logoff, and need to know if 
there's any way to do that.

Now, of course, I could just yell at him to get off the computer, 
but I'd like to do this more subtly than that, and encourage him 
to keep track of his online time so as to avoid having an automatic 
logoff message sent to his friends.

All suggestions welcome. TIA.

Bill Horne