Where can I find a Time Restricted Keypad Lock?
Schlage has a Schlage Link line of locksets that you may want to check out. It offers remote security if you have a wireless network and an internet connection. The link below is for the Lever lockset starter kit.

http://link.schlage.com/Products/Pages/KeypadLeverStarterKit.aspx

Other options would be to search for locksets under "Home Automation".  

Update:  Below is a link to a gateway/controller with no monthly access fees (unlike the Schlage above).  You would need to purchase either Schlage lockset and the gateway/controller.

http://www.micasaverde.com/vera.php