We recently fixed a bug where the users timezone was not properly saved in the users’s settings.
Furhtermore there is no possibility in the ui for a user to choose the time zone - we will work on this in the future.
To see what timezone of a user is used (replace admin with the user id you want to know about):
./occ user:setting admin core timezone
As a quick work around you can set the user’s timezone like this:
./occ user:setting admin core timezone --value Europe/Berlin