Off late I was trying to find information on the users license and I found out there are licenses names Concurrent Cals and Session Cals, however the document that I got from the internet was not that beneficial.
Can somebody please help me with more information on this CAL's.
From version 11 a Session CAL will work as a Concurrent Session CAL. The change is simply from counting document sessions (one user opening up one document) to counting user session (allowing one user opening up multiple documents).
With one Concurrent Session CAL one user could open multiple documents. When the session has terminated (min session length is 15 minutes) this could be used with another user. So the answer for your question would there by be one and there is no maximum length unless the user is inactive and the server setting will terminate the session.