Internet time access

Hi

I want to know if it is possible to set the time available to users for accessing thr Internet. Ex from 09:00 to12:00 16:00 21:00.
I am working in a Win 2000 domain, but I am not providing the internet server connection. I do have policies for my users but I could not find a policy to set the available time for Internet access.

Thanks
Melt