When you don't check the remember me box your login relies on a session cookie. Whilst that cookie will not reside on your PC it resides on the server to maintain your login state.
The default session cookie timeout on vbulletin software is 900 seconds. Your timeout I would imagine would be refreshed upon page load, so if spending >= 900 seconds on a page without page load will time your session out and therefore log you out.
|