Have a look at the Automated Logout module. Some details about it from its project page:
... provides a site administrator the ability to log users out after a specified time of inactivity.
It is highly customisable and includes "site policies" by role to enforce logout.
Features:
- Different timeouts based on role.
- Disabling of timeouts based on role.
- Permission for users to set their own timeout.
- Includes some JS mechanisms to keep uses logged in even if multiple tabs are open or if the user is working on a form for a long period of time.
- Includes developer hooks to allow users to remain logged in depending on your own project specific requirements.
- Optional integration with Javascript Timer.
If you limit your specific pages to be accessed only by "role", using this module should help. If needed using the available hooks to further refine its logic to meet your specific requirements.
Refer to the article about Auto Logout for some more details (and screenprints) about it.