When my Google Analytics account shows 10 minutes for time spent on site, what does this mean?
Does it mean the visitors have opened one page and left it idling in a tab while (possibly) browsing in another tab?
Or does it mean they have been browsing my site for 10 minutes straight with at least a certain amount of actions within a specific amount of time?
I couldn't find any explanations of what exactly it is they measure.
Google Analytics uses the following definitions :
The time on site for a particular visit is the sum of the time on pages for all pages that constitute that visit.
The time on a page for a particular page is :
calculated by subtracting the initial view time for a particular page from the initial view time for a subsequent page
as pointed on http://www.google.com/support/analytics/bin/answer.py?hl=en-GB&answer=99118. Google Analytics uses the timestamps of the GIF request to calculate the 'view time'.
That means that the last page that a Visitor visited, as it does not have a subsequent page, is not taken into account in this calculation.
It is also good to remember that a visit ends after the Visitor either closes the browser or after 30 minutes of inactivity.
From Reverting Back to Original "Average Time on Site" Calculation Today, the amount of time spent on a website is calculated from
[...]the total time on site for all visits divided by the total number of visits
