Getting a user's time/duration in a meeting might work using the session resource type API call. However, our Microsoft Graph API documentation with Microsoft Teams should explain more on this. I have also added the respective "teams" tags to this thread so someone from their team can further assist on this issue if needed.
If you'd like to create a feature request you can do so using our MS Graph User Voice Forum.
Working with the communications API in Microsoft Graph
If you have any other questions, please let me know.
Thank you again for your time and patience.