In my Knowledge, the total time spend on the site is calculating by taking the time between the first and the last hit (server call) sent to Analytics.My Question is when will be the last hit happen if a visitor comes to my site , with out further interaction he closed his browser. in this case how the last hit happen ? and how this total time reflect for calculating the average time spent on site .
As indicated by ForgotPassword4, the time spent on the last page/interaction is not counted. However, there is a way around this in some cases.
The "last page" is typically the last one the user sees before leaving the site. So on domainA.com they click a link that goes to, say, domainZ.com. You can create a function to generate a custom link type call (pe=o) if the destination domain is different from yours. This provides an "exit" call that will allow the time spent calulation for the last (real) page.
In our case, we typically have an exit pop-up on our site that accomplishes the same thing.