Hi  This is interesting however i noted this definiton for aggregated task time :

Combined time it took to execute the query across all cores of all nodes. It can be significantly longer than the wall-clock duration if multiple tasks executed in parallel. It can be shorter than the wall-clock duration if tasks waited for available nodes.

so basically, 

The aggregated task time is not related to the execution time but the sum of all individual task time.ex: if you have 5 tasks each ran for 1min in parallel then The execution time might be 1 min but the aggregated task time would be 5 min