You have two options in the settings file that should allow you to configure the session timeout however you wish,
* Set session lifetime (in seconds), i.e. the time from the user's last visit
* to the active session may be deleted by the session garbage collector. When
* a session is deleted, authenticated users are logged out, and the contents
* of the user's $_SESSION variable is discarded.
* Set session cookie lifetime (in seconds), i.e. the time from the session is
* created to the cookie expires, i.e. when the browser is expected to discard
* the cookie. The value 0 means "until the browser is closed".