Hypothetically, suppose someone came to you and stated that they have been living in Australia for a while and since it's timezone is ahead by x number of hours, during that time they've been living in the future.
Obviously it's ridiculous, but how would you reason with them that they're wrong?
My reasoning would be that time zones are a human artifact, created due to the rotation of the Earth to ensure that certain points in the day, such as noon happen when the sun is in a certain position in the sky, are the same at all points on Earth (by this I mean that midday is always when the sun is straight overhead, wherever you are on Earth). As such, it cannot have any effect on the physical passage of time.
Importantly, the notion of "present" is the same no matter where you are located on Earth - time passes at the same rate at all points on Earth. An event, such as a flash of lightning, at one point on Earth, occurs "at the same time" for observers located at any point on Earth, it is simply that they have labelled the particular instant in time with different coordinate values (one shifted with respect to the other). The point being that what happens in the present for one observer on Earth, happens in the present for all observers on Earth (it doesn't happen in the past for some, the present for others, and the future for another).
Would this be a reasonable argument?