Is it possible to change a session's or account's lifetime

Hi, What I want to do is temporarily allowing a user's access for a short time, say 2 minutes, and if the user takes further authentication process, the user's access can be allowed without limit. I tried to use the Expiration attribute in radcheck, set the value to be 2 minutes later in the beginning, and set it to be 1 day later after the required authentication process is completed. But it seems the NAS only reads the initial value. It expires the user in 2 minutes and never reads the new value. So the question is how to limit and change the lifetime of a session or of an account? Thanks for your help.