I see one place this is available for me.
Go to Office.com & sign in.
Click on your name in top right and select My Profile.
Look to the middle left. Click on the "Update Profile" button.
Scroll to the bottom of the Contact Information section.
Click on "How can I change language and regional settings?"
Then you'll see: "Click here, click the ellipsis (…), and then choose Language and Region."
As per that hint, click on that "here".
On the "Edit Details" page that comes up, you'll see headings - Basic Information, Contact Information, Details, and ...
Click on the ellipsis (…) to the right of the word Details.
Select Language and Region.
In Region, select "Always use my personal settings"... (If you don't know what you're doing, then caveat emptor.) If you don't do this, you can't select your time zone.
In Time Zone, select "Only Me" on the right and then your time zone.
Click Save & Close at bottom of screen.
