Without high speed travel, I'd assume that people wouldn't realize the existence of time zones at least for a while, so what is the earliest known instance of the acceptance of time zones?
Time zones are an arbitrary construction, but people in classical antiquity realized that time was different in different places. I wrote about this before: https://www.reddit.com/r/AskHistorians/comments/3uufv2/when_did_people_understood_the_concept_of_time/