Timeout value sets the length of time after which inactive users are automatically logged out of the system. The options are between 15 minutes and 12 hours.

The value of the last active session is not updated until halfway through the timeout period. So, if you have a 2-hour timeout, the system does not check for activity until 1 hour has passed. As an example, say, you have a 2-hour timeout value. If you update a record after 30 minutes, the last active session value is not updated because there was no activity after 1 hour and hence, you will still be logged out in another 1 hour and 30 minutes, because the last active session has not been updated.

The Disable session timeout warning popup feature sets whether inactive users are presented with a timeout warning message. Users are warned 30 seconds before the session timeout, as set by the timeout value.

Enabling Force logout on session timeout option causes inactive users to have their browsers refreshed and set to the Salesforce.com login page when the session times out.