I am trying to track Avg time on page on a specific page where the conversion event is to click off to a clients micro site. My understanding of for calculation for the Avg viewing time is the timestamp of the last activity in the session minus the timestamp of the first activity. Therefore, when a user exits the website the final page does not get an accurate Avg viewing time. Can I add a page level tag to fire on unload to track this? If so, how would you suggest I accomplish this?