I was able to reproduce the issue. The total duration below is correct, but the sum of the Duration column is way off.

Total Duration in Minutes: 273 (4.5 hours)

Sum(Duration) in Minutes: 3476 (57.0 hours)

Check my query to make sure I'm not doing something stupid (it happens from time to time).

select ((datediff(MS, min(starttime), max(endtime))/1000)/60) as "Total Duration in Minutes",

(sum(Duration)/1000000)/60 as "SQL Duration in Minutes"

from temp_trc

I'm at a loss, and haven't been able to find anything explaining the discrepancy.