A major change to the session system is currently being tested.
With it, users should no longer time out.
If you have your "Keep me logged in" box checked, this should have no effect on you. If you do not have this setting checked, there are now only two (not three) ways to log out: 1. hit the logout button, and 2. close (exit or quit) your browser.
Please report any problems anyone observes with this change, or voice your general feedback in this thread.