I placed a time limit on my AirPort Extreme and now I can't access my airport utility to disable it because I can't connect to the Internet?

Soft reset the Airport.. it will go back to defaults for 5min so you can fix it.

Since Timed Access only applies to wireless connections, an alternate plan would be to use an Ethernet cable to connect your computer to the AirPort router and then use AirPort Utility to change the wireless settings.