a predefined list of valid timezones is given
perhaps a useful link:
https://gist.github.com/kirley/3913166
This will not be available via our own nominatim service:
https://trac.openstreetmap.org/ticket/4200
There is more or less a consensus in the OSM community that timezones don't belong into OSM.
So, the same goes for Nominatim. It simply won't happen.
In March 2020, pytz (and geocoder) were no longer used for timezones and states!
This information is now obtained from http://api.geonames.org/.