It's in the Advanced setup section. Actually your router is a bit confusing, from what I am use to (and that is a lot of different routers of different makes and models).
You can allow and deny access at certain times of the day or all day everyday.
Turning off the DHCP server is a sure give away someone is screwing with the router as the computer won't get a IP assigned to it and neither will any printers or other devices on the LAN. Restricting access makes it look like they are connected, and they are to the LAN, but can't use the internet.