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

[张强]

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.