PieChart and Time Spent

PieChart and Time Spent

Hello! We want to make a report with chart for us.
So, we did a report with time spent, and in that report we make PieChart 2D with axis column - category. And we have this:
So here all requests of tehcnican for 1 day by categories. But we don`t want in that chart quantity of request by category. We want spent time of technican by category. How we can do it? 
Thank you :)

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