idletime in login.conf

[Modulok]

List,

Goal: Automatically logoff users that are idle after 'x' minutes.

Attempt: I added this to /etc/login.conf to the default login class:

    :idletime=10m:

I then rebuilt the database:

    cap_mkdb /etc/login.conf

Problem: It doesn't work. The 'w' command shows users idle for 20 minutes or
more. I'm missing something. Other than an autologout shell variables, how do I
force idle users to logout?

Thanks.
-Modulok-