Linux based gateway for time-based wireless service.
 

Has anyone heard of basic software packages for managing internet / network access via MAC address, which can be set via an administrator for sections of time. For example, the system would be put between a networ with a gateway to the itnernet, and a separate subnet containing wireless acess points. the linux box could run iptables with a frontend/job running evenry minute to check for newly added entries permiting a MAC address access to the other network with internet access?

I know it could be done with a good bit of scripting, but i'm pretty sure someone has done something comparable or better out there already.