Unfortunately, Enterprise Reporter (ER) cannot report on user log off times, even after extending the attributes collected by ER and adding the "last-logoff" attribute as this attribute is not populated by Active Directory.
The Intrust product can provide this information. InTrust collects user logons and logoffs from Security logs of computers they are logging on to. It also has its own user session tracking mechanism.
For more information about Intrust please see the following page or contact your Sale rep: