To run Ansys applications, each application will poll the License Manager for and check out the required license increment when launching.  Additional features within applications may require additional license increments to be used.  

Users can continue to run multiple Ansys application sessions until they have exhausted the available license increments in their pool.  The users who have the license in use are visible from the License Manager, and if the license increment needed is not available, the user may receive a denied error message that all licenses are in use, or that the license does not exist in your pool.

This is an example of a license increment being checked out when launching SpaceClaim, viewable from the License Manager, under Current License Usage, formatted Name (increment), showing Ansys Mechanical Enterprise (ansys) checked out, as well as the user who checked it out:

Once the work/project is saved and SpaceClaim is closed, the license will return to the pool of available license increments and the user that had checked out the license is no longer visible:

License usage can also be viewed live from the License Manager server using Powershell (increment only), and historical data in the License Manager logs (increment only):

 While using Ansys applications, there is repeated communication with the License Manager to ensure that the required license increments remain checked-out to the user using the application, referred to as the Heartbeat.  The Heartbeat occurs every 5 minutes and will provide a warning to the user if the License Manager cannot be reached.   If this persists for 60 minutes (default), the License Manager will be deemed unreachable, and the application will revert to a read-only mode until a new connection with the License Manager can be established (most applications).

Related articles 

ERROR - License Server Lost for X Minutes

HOW TO - Test & Fix License Manager Connectivity Issues

Alternative method 

HOW TO - Borrow an Ansys License

License timeouts can occur in a few situations:

1. When launching Ansys applications - applications will poll the set license server for active licenses on startup.  For example, Workbench will poll the license server at launch and populate the Toolbox based on what's available in the current license.
   
   
2. If the Licenser Manager server connection is lost during application use - this is based on the Heartbeat functionality noted in the previous section.  If lost connection persists for an extended period (default 60 minutes), then the application will prompt you to save your work, before it reverts to a read-only state.
3. If the application is left idle for an extended period - if a user is working in an application and the computer is left idle for an extended period, the checked-out license will be automatically checked back in and made available for other users.  The application will attempt to check out the license once again when the user session is no longer idle.

Related article 

ERROR - Connection Timed Out While Reading Data

HOW TO - Modify the License Timeout Setting in Options File