You could do a SQL query to pull the durations and sum them. Also if you look at the "TIME" column of the Test Grid for a specific test set and subtract the earliest time from the latest time you can get an the overall time then add the duration for the last test run in the test set, since the times shown are start times only.
We use a third generation Key Word tool and it records the test set duration. But I wouldn't buy it for just that application.
Success is the ability to go from one failure to another with no loss of enthusiasm.
~ Winston Churchill ~