I know if you check the "Always stay logged in" box, the cookies are set to expire in the year 2038. If you don't check that box they expire in a few hours and you need to login again once they expire or anytime cookies are deleted from your browser.

The "Minutes to stay logged in" is confusing. It's somehow remembered and used by the guts of the board. Setting it low has some effect on names in the "Users on line" display but it's not exact. Setting it to 5 seems to last 10 and using 120 seems more like 30. Guests are counted for a few minutes after their last click.

As far as logging in and out goes though, logging out deletes the cookies from your computer, your name from the online display and requires you to login to access member options again. If you check "always stay logged in" your name in the members online display disappears sometime after your last click and I believe the name of the most recent click is listed first.