I recently loaded some old observations and as per the new Time Zone assignment, based on the coordinates, the time zone was assigned correctly. All of the other existing observations for that day had a default time zone of EDT which was the default time zone in my profile when I did the initial upload. The date and hour in the EXIF of the old observations was for a different location (not EDT) which I forgot to reset to the new location. So three time zones, the time zone in the camera, the actual time zone of the location and the time zone in my profile EDT.
I decided to fix the time and time zone in the old observations for consistency. I edited the observations to the correct time, typed in the new time zone and saved the edit. The time changed correctly but the time zone stayed as EDT. I found this frustrating but then recalled that the new process for defining the time zone is by the location of the observation. So I edited the observations (individually) and changed the location by changing the last digit in one of the coordinates i.e 24.862455 to 24.862456 and saved the observation. Voila the correct Time Zone was assigned. The time data for that day is now consistent. A change to the coordinate in the 6th decimal place has no meaningful impact on the accuracy of the location.