This feature is not supported now.
You can only get the duration of callings and meetings for the latest month in Teams admin center > User > Call history.
I have created a feedback about this feature by this link: https://microsoftteams.uservoice.com/forums/555103-public/suggestions/41825341-i-want-to-get-all-the-duration-of-call-and-meeting. You could vote for it.
Microsoft will always focus on customer’s feedback and experience. Some new features would be added to the services based on customers' feedback in the future, and your good ideas will be very helpful for them to improve the service.
Your time, understanding and cooperation will be highly appreciated.
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