Average Time on Site, when used against individual pages as in your example, show the average time spent on that page (calculated based on each page view).
The documentation shows an example of the calculation:
https://experienceleague.adobe.com/docs/analytics/components/metrics/average-time-on-site.html?lang=...
But in simple terms, whether the page was viewed by the same visitor, or within the same visit, each time lapse calculated between pages views would be used to get the average:
- Page A - View 1 - 1 minute 10 seconds
- Page A - View 2 - 1 minute 30 seconds (consecutive view from view 1, therefore the "time spent" would actually be treated as 2 minutes 40 seconds in total)
- Page B
- Page A - View 3 - 30 seconds
- Page C
- Page A - View 4 - unknown (as last view in the visit)
View 1 and 2 are added together in the total as they are consecutive (2:40)... then View 3 (0:30) would be added together and then divided by 2 to get an average of 1 minute 35 seconds (View 4, being the last view of the visit, and not having a time lapse would be excluded from the average time calculation.