When exactly did people understand that at the exact same moment it might be early morning e.g. at Rome, but noon in central China? Had they understood that from planetary motions or could they have deduced it some other way?
While someone is writing a response to this question, you can read over the previous discussion and answer from u/krangs on a related topic about the history of time zones: https://www.reddit.com/r/AskHistorians/comments/3uufv2/when_did_people_understood_the_concept_of_time/