The AirPort Extreme does allow for timed access of wireless clients connected to it. With this feature you can control when a wireless device (by its MAC address) it can have access to the network.
You can find this feature in the AirPort Utility. ref: AirPort Utility > Select the AirPort Extreme > Manual Setup > AirPort > Access Control > MAC Address Access Control = Timed Access
Your Extreme can set time restrictions on when specific computers can access the network. You can configure them using AirPort Utility:
Open AirPort Utility, select your Extreme in the sidebar, and press "Manual Setup." If you're asked for a password, enter it. Go to the "Access Control" tab and set "MAC Address Access Control" to "Timed Access."
Now you can set up the time restrictions.
To add a computer to the list, press the "+" button. You'll be presented with a dialog that will let you configure the time restrictions. You'll need to enter the device's MAC address. You'll also want to enter a description so that you'll know what device the restriction applies to.
You can double-click the "(default)" entry to set restrictions on computers not on your list. When you're finished, press "Update" and allow your Extreme to restart.