It helps, when we always display the date &time with the timezone. That makes it easier to compare times.
I have changed the System Preferences > Language & Region > Advanced > Times for the Medium format to include the time zone suffix. This way I can see easily in Photos, which time zone is used to compare the timestamp of a photo with other photos.
This is working since macOS 10.15 Catalina and described here: How to display the Date and Time Zone in the Info in Photos in Catalina
For example: The info for this photo is showing that Photos is incorrectly using the timezone of the Galapagos Islands (-5:00) for the time stamp of the photo, because the photo is tagged with GPS; showing it has been taken on the Galapagos Islands. My cameras are always kept on UTC, so I have to change only the time zone for the photo without changing the time.
