FreeRADIUS Version 1.1.7 on Novell SLES10

The question is simple but I can't seem to find the answer to it so I will apologize in advance.

Can some one tell me the format for entering the date in the Expiration attribute?

I'm using the users file to authenticate users on a small wireless network. ie.

testuser        User-Password == "testpass"
                Expiration = ???  (lets use today 10 October 2007 as an example)

thanks in advance.