Expiration account

Hi, I got Freeradius working with Chillispot and Mysql. I would like to create account with expiration attribute. For example, I would like to create account with a validity of 24 hours after the first connection. And i would like do to the same with validity of à week. I tryed to done it with PhpMyprepaid, but the way to do it is not clear for me. If someone can explain me how to handle this problem. I know that i have to activate "POSTAUTH" in Radius.conf and to insert a query in Mysql.conf. Thanks in advance