Rasputin - 7:27 am on Jan 8, 2012 (gmt 0)
As for Google analytics, it can only measure time between first page and last page. If a user only views one page, the analytics see that as "no time", even if the user spend 10 minutes on that one page.
In the new(ish) google analytics 'real time' feature it looks to me as if they are measuring quite accurately both arrival on the page and time spent on the page as well as subsequent activity on the site i.e. recording how long someone stays on a page within the site, whether they are looking at just one page or looking at several.
Is that not the case?