[Max Taxable]

The "remember me" box when checked installs the lifetime session cookie on your browser, keeping you logged in through multiple sessions until you click the "log out" link.

If the box is not checked, you get the default session cookie which expires after the time set for it in AdminCP, whether you log out or not..

This is so users can choose whether the device they are on stays logged into the forum, if they are on a public device like a library computer for example, they would not want to check the "remember me" box.

If you are being logged out before the time set in AdminCP, it's likely your browser security settings are responsible. Some browsers routinely "crunch" session cookies depending on settings. This is overcome when you permission the lifetime cookie.