Hello everybody

I am looking for an option to use the m0n0wall in a lanparty 
environment, where I want to restrict the internet access to the 
visitors with the captive portal, but based on the time of the day 
rather than just by the date. I want to say: "Okay you may access the 
internet with thisandthat username/password until 8.00pm". Is this 
possible, if not: Is there a known modification or something to do this? 
If not, too, maybe that's a nice feature to have?

Greetings
Carsten Holbach