I did the same, I changed the timezone to Sydney in Teams app and online, Outlook app and online. I even reached out to my admin and saw the timezone and location set to Sydney, Australia. We even checked in Azure and I restarted Teams, Outlook and the laptop several times now and my timezone on Teams STILL shows up as 18h ahead.
I am on macbook and the timezone is set to Automatically based on my location and I even changed that and set manually to Sydney, Australia even then it didnt work and STILL shows as 18h ahead.
We even tried and saved a different timezone (say Canada) and saved and restarted etc and then changed it back to Sydney, Australia and saved and restarted and its STILL showing 18h ahead.
Now in the Teams I have seen the timezone option and the option to set the work hours, even there its set to UTC+10 hours Canberra, Melbourne, Sydney but the Teams STILL shows 18h ahead.
At this point I am so frustrated and whenever any of my team members setup a meeting theyre always shown a warning that its out of my working hours etc. I think Teams and in general Microsoft products are utter ****. Even my admin is pulling his hair out why its like that and its not only me but several other people facing this issue.
This post should not be marked as SOLVED because its NOT solved.