Need Linux Router

I have a Debian Linux box on a network that needs to act as a simple router with a couple of extra features.  Network A is on the main LAN interface.  LAN A has an internet router whose address is set as the default gateway for the Linux box.  Network B will be on a secondary LAN interface with a small handful of devices.  I need all traffic between the two LANs to be freely forwarded, but I need traffic from LAN B to the internet to be completely restricted to the hours between midnight and 5:30 AM.  My client has a metered internet service that is free between those hours, but carries a fee outside those hours.

I need the router not only to restrict all traffic to the internet between those hours, but to also log any attempts to engage in traffic outside those hours and to meter all traffic to and from the internet at all times on LAN B.