Time zones were actually invented by a Canadian, Sir Sandford Fleming, in 1878, to solve the inherent problems of scheduling railroads without a standard time. Before standardized time and time zones, everyone declared 'high noon' locally, as the sun was exactly overhead of where they were. Time zones were based on the concept of 'high noon', but standardized within regions.
If one is not at all inclined to be constrained by the concept of 'high noon' being exactly 12:00 when the sun is directly overhead, then really one only needs one time zone for the entire planet. Otherwise you chose the number of time zones that closely achieve your objective of 'high noon', the sun being directly overhead, and the time being 12:00 to be within your parameters of acceptability. Is a sun that is 20 degrees offset from 'high noon' an acceptable alternative to '12:00'?
The closer to 'high noon' you want to get to, as the sun revolves around the earth, the more time zones you need. The reduction to absurdity, of course, reverts back to the original 'every town has its own time zone'. You set the allowable divergence to high noon, and you go from there. Sir Sandford Fleming arbitrarily broke time zones up by the hour, when in fact he could have done it by the half-hour, or fifteen minutes, or even every two hours. The objective and the result was a trade-off between ease of calculations, number of railroad 'localized schedules' necessary for a long cross-country trip, and conformity to 'high noon'. That depended a lot on the geographical width of the country. Britain, everything fit in one time zone. Canada, not so much. But ten schedules across the nation? Two? Five? The choice was arbitrary but easily calculated to be 'every hour'. Newfoundland, of course, was the exception.
A decade or so ago, time zones were pretty much dictated by television scheduling - "News at 11, half an hour earlier in Newfoundland'.
Prime time scheduling was the same time, everywhere. Almost.