Test Execute License Timeout
If that's how you operate, then that's fine.... but there no automatic settings to release someone's licenses that I can find. So, these will have to be manual controls you put in place... powershell command to reboot those machines every night at a set time for example would work.
Another option... rather than you're integration testers manually running TestExecute and then doing the whole "right click and run", you could set up a list of shortcuts in a folder that would be batch files executing TestExecute commandline instructions that would execute the tests and then exit using the /exit commandline switch. This will ensure that TE is shut down automatically after each test execution.
Generally speaking.... most shops that I know of only use TestExecute for automated execution, not for having other testers run the tests. Seems.... counter intuitive to create an automated test scenario that a user then needs to manually kick off...