As you can see in the below *M365 Admin Center Teams Usage Reports** Section screenshot, Last Updated Date (or Report Refreshed Date) is of UTC date & time format. "Last Updated Date" in M365 Admin Center Usage Reports section is same as Report Refreshed Date in M365 usage report Graph API response as shown below and hence {date-value} is of UTC date & time and it must have a format of YYYY-MM-DD.. Currently Teams User Activity User Details report only includes date only (without time) such as Report Refresh Date, Last Activity Date..etc.
Example : GET https://graph.microsoft.com/v1.0/reports/getTeamsUserActivityUserDetail(date=2021-12-14)
The above query generate **Teams User Activity User Details** report of all the users on the date 2021-12-14 in that tenant.
Example of Teams User Activity User Details report :
Hope this helps.
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