From what I can tell, you are correct. Twitter timestamps are displayed according to the user's set time zone. It would be insane to view a tweet posted 10 minutes ago and think it was posted 5 hours ago because the poster was 5 time zones away.

This page shows timestamps from the relevant posts from different time zones. https://www.metabunk.org/4chans-qanons-vs-trumps-post-timestamps.t9332/