I ended up finding the solution to this problem in some other information here and The JTB website
& this link below:
http://usa.autodesk.com/adsk/servlet/ps/item?siteID=123112&id=7459915&linkID=9240617
Solution
Access to licenses is controlled with a FLEXlm® options file that is configured with the settings you want to use. The options file is an optional component of the Flex license management system and is not required for normal license operation.
Creating the options file
1. Create a new text file named ADSKFLEX.OPT. It is strongly recommended that you only use a plain text editor, such as Notepad, for editing options files.
2. Place this file in the same directory as your Autodesk license file.
3. Perform a ReRead License File operation from the Start/Stop/ReRead tab in LMTOOLS.
4. Examine the debug log file to confirm that your options file changes have been implemented by the license manager.
My ADSKFLEX.OPT options file has one line:
TIMEOUTALL 1800
If you have left AutoCAD open but not used it for 30 minutes, the licence will be freed up (so others can use it) but AutoCAD stays open but inactive.
When you need to use the open AutoCAD again, it gets another licence (if one is available) and all the drawings are how you left them.