Adding A Time Zone Column In Your CSV File.

What's the proper way of formatting "country" in a CSV file? How to bulk upload prospects with the right timezone parameter?

You can use the following standards to set a timezone :-
1. For country names follow the country name column in this standard:

2. Timezone needs to be in the Olson timezone format:
https://en.wikipedia.org/wiki/List_of_tz_database_time_zones. Check the second column "TZ database name" in the list in the link above.