This document helps me know how to track logins and logoffs: http://answers.splunk.com/answers/108923/how-to-track-a-specific-user-login-and-logoff-the-past-30-d...
However, in my organization, no one really logs off from Splunk. They just close the browser window or shut off their computer. Is there a good way to track this action?
This is not unique to Splunk. It is the nature of IP and HTTP protocols - they are stateless. So, you cannot really track a 'session' since there is none to track. Each request is treated as an independent transaction.
More information can be found at http://en.wikipedia.org/wiki/Stateless_protocol
No, because Splunk has no way of knowing whether someone closed the browser window. All that happens is that requests stop coming from the browser.
so is there a timeout for the login? And then the user is forcibly logged off?
Not so much "logged off" as that the user's session expires and the corresponding session cookies are invalidated. This is not logged anywhere that I know of.
Yes, that is configurable. More details here..
http://docs.splunk.com/Documentation/Splunk/6.2.0/admin/Configureusertimeouts