Thank you Mark, it is a much needed routine on my site.
Please promise that in future iterations that you will provide a 'pop up splash page and logon' and the create a way to allow the Admin to send themselves a cookie that will exclude them from the timed limit. I like to browse my entire site as a guest sometimes, checking to see it the way a guest does.. Ten minutes... delete cookies... ten minutes.. delete cookies... ten minutes... delete cookies.. arrrrgh!

The splash page could see more pop-up like the current 'logon' box does.. allowing the user to cancel that with the little 'x', and then continue surfing for a few more minutes, when it pops up again it cannot be canceled (the x is gone, etc... )