TimeSpent Report - Pie Chart

TimeSpent Report - Pie Chart

Hi everybody
I have a small problem/question : when I create a new custom report for TimeSpent for our technicians, or when I use a predefined report, it appears that the chart count the number of requests, and don't sum the time spent on the requests.
 
Is it possible to change this, and could sum the time spent on these requests ? And, if it's possible, how can I make this ?
 
I have searched on this forum, but the calls with this problem have no answer/solution to this problem.
 
Thanks
Best Regards

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