I believe these two metrics (average time on site and time spent on page) are not measuring exactly the same thing, and some of the logic behind how Adobe Analytics calculates time metrics is likely causing the discrepancy.
Average time on site:
From what I understand, the 'average time on site' focuses on the average time spent per session across multiple pages and excludes the last hit, which can create a higher average time if there are bounces.
The metric looks at sequences of hits (eg. user interactions) and calculates the time difference between consecutive hits within the same visit.
If there is no subsequent hit after the dimension item (e.g., the user leaves the site or session ends), the time spent on that last page is excluded from the metric.
The metric can be tied to specific dimensions, such as pages or sections, and calculates the time spent between hits that contain that dimension.
'Average time on site' is good when you want to see average time spent for specific dimension items.
Time spent on page
'Time spent on page' dimension seems to only measure the time spent for each individual hit, also excluding the last hit. As a result, it captures all page views, including those with very short durations. This would be leading to a potentially lower average when aggregated across many visits.
Time spent on page' is valuable when you want to understand how long visitors interact with a given metric on your site.
I think in relation to the 11 Seconds from time spent on page. Then it may include many short durations from visitors who quickly navigate away from pages.
I hope this helps you!
Check these out:
https://experienceleague.adobe.com/en/docs/analytics/components/metrics/average-time-on-site
https://experienceleague.adobe.com/en/docs/analytics/components/dimensions/time-spent-on-page
