So I’m a little confused here. Once the web uploader is told the geographic location of the observation (either manually or from EXIF geotags), it should automatically know the time zone where the observation was taken, and be able to apply that to the observation without any user intervention.
What the web uploader won’t know is whether the user remembered to change the time on their data collection device (smartphone, DSLR camera, etc.) to match the local time where they were, or left it set on their “home” (or some other) time. In that case, one would want to be able to tell the uploader, no, the time on this observation was not local time, it was from time zone X instead. Once it knows the correct time zone to associate with the time recorded on the observation, then it could automatically adjust to the local time zone of the observation, or the user’s home time zone, or whatever time zone they prefer.
So where a time zone chooser would be needed, I’m thinking, is associated with a question, what time zone does the displayed observation time represent?, with the default being the local time zone of the observation (once location is known).
Is this already what you had in mind, and I’m just overthinking it?
It seems to me that the time zone set in the user’s account setting should only affect how observation times are displayed, not how the data are interpreted at upload. Otherwise that makes things very confusing. And there should also be an option, as part of that same account setting, to always display times using the local time of the observation, instead of having to pick a single time zone for all of one’s observation.