Restating and elaborating on my previous reply for clarification:
The auth session token is saved for 14 days (default). If a user signs out, if the device kills or terminated the process, or if the network access is terminated, the SP token expires.
Meeting Center can be configured in Super Admin to adjust the timer. I believe you can also do this in the IDP config. Whichever timer is shorter is the one that will be in effect.
Hope that helps.