This happens a lot with landing pages because many times there is no 2nd page view as people don't convert. In landing pages this metric is super important. If a person left after 5 seconds your page is probably ugly. If a person leaves after 1min your content might not be convincing enough or no clear call to action. You need to know when people usually leave your page in order to know how to fix it. In http://www.pagealizer.com/ we track the time spent on page (beside other metrics) by pinging the visitor.