6
If you are using the default XOOPS session, if a user logs in and is idle for about 20 to 30 minutes the session will timeout by default. As long as the user is active, it should not timeout on them.
You could try a custom session, or an auto logon hack. But if they are active for that time frame and still times out there is another problem.
Now, remember that the auto login does not keep sessions active, it just logs you on automatically.