The average time spent on the page, from the first page view trigger to the last event sent.
How it's calculated
Time Spent = (Time of last event sent) - (Time of first pageview sent)
How to interpret it
This is how long users spend on a page and is good to think of in terms of content consumption vs. a PDP page, the latter of which users should not be on for as long as they would be on a blog post or the like.
Keep in mind, when you create custom segments to filter by users who viewed your page for a shorter duration. e.g. Users who spent <10 seconds on a page, the metric will include all pageviews for the session not only the pageview with the short duration.
Significativity
It is not recommended to use this metric on low views. — On a small sample, time metrics are highly likely to have a high variance: some users can spend 10 min or more on the page before clicking an element, which makes the average time highly skewed if you have any extreme value.