Represents the average amount of time visitors interact with a specific dimension item during each visit.
Average time spent on site (Seconds)
Represents the total amount of time visitors interact with a specific dimension item, per sequence with a dimension item. It is not just limited to “site” averages as the name suggests. See How Time Spent is Calculated section for more information on sequences.
Note: This metric will very likely differ from Time Spent per Visit at a dimension item level due to the differences in the denominator in the calculation.
How does Average Time Spent on Site differ fromTime Spent per Visit ?
The difference is the denominator in the metric:
Average Time Spent on Site uses the sequences that include a dimension item.
Time Spent per Visit uses the visit count
As a result, these metrics may yield similar results at a visit level, but will be different at a hit level.
Your hypothesis would only be correct for 'Time Spent per Visit', if users only have one sequence per dimension item within the visit. Otherwise it looks like 'Average time spent on site' is the metric to align with your interpretation.