This suggestion did it! I created a new group Non-Administrators from Computer Management-> Users and Groups-> Action-> New Group and added all the non-admin accounts to it to create a Non-Administrators group. Then I ran MMC, added the Group Policy Editor, browsed for a Group Policy object, and selected Non-Administrators. I was then able to set the session timeout after disconnection. To make it work I had to disable Session Timeout for the computer and for all users using gpedit.msc, as these seemed to override the group policies.
Thanks for the quick response - this question has been unanswered on Microsoft's Technet for a number of weeks