I am seeing the same problem in the Mac version of the new "Microsoft Teams (work and school)"
I have tried:
- logging out and back in - Did not help
- Changing my timezone to something else and then back to Mountain Time here:
https://myaccount.microsoft.com/settingsandprivacy/language and then restarting the app - Did not work
There does not seem to be a place in the app to change my timezone.
What else can I try?