Add info on application/session timeout screen about lowest usable timeout values

[mpwoodward]

Since the background process to check for session/application timeouts only runs every two minutes, add a note to the application/session timeout screen letting people know that values below 2 minutes won't have any effect.

Might be worth adding this as a configurable setting in the engine I suppose, with a default of 2 minutes, but then if people really need something with more precision and want to accept the overhead involved with the background process running more frequently, they could configure it.