What are you seeing in your Connections Overview as far as licenses in use and when they expire? I ask because we are on 6.11, and sessions automatically time out after about 12 minutes of inactivity in the web client. More details have been discussed on this thread:
I have not figured out why some folks seem to have connections which will not release, but ours do release. It might be related to a module (e.g. Workflow) keeping connections more "alive", but that is wild speculation on my part. Check the connections in your DW Admin tool and see what happens to expiration timestamps for idle connections. They should drop from 30 minutes from start to just two minutes from the current time after ten minutes of inactivity -- that is what I see in my 6.11 on-premise system.