>Something I've wondered about though - since I never "logout", how does UT know if I login at 13:30 if I am still logged in at 14:30. I know a cookie will expire eventually but it seems in real time UT doesn't actually know who still has their browser open and who doesn't.

It is based on the activity not at the time of the login. So, for as long as your browser remains logged to UT, this creates activity. Cookie on the site lives for the duration of the browser. They disappear after. There is no expiration. If you would wish to remain logged to the site and not close your browser, you could be logged for weeks and that would do.