i think your account should always have a default time zone specified. whether it is assigned correctly initially or not (or how it should be assigned) is another question, perhaps. currently, i think it works as described here:
if that’s a bad workflow, maybe the best thing is to propose a better workflow in a feature request?
or if you just want to change the basis for time zones added to observations, then maybe that’s covered by https://forum.inaturalist.org/t/add-time-zone-chooser-to-the-web-uploader/3096 (unless you have a different proposed workflow)?