The central latitude of the continental US is about halfway between the equator and the North Pole. I don’t remember geometry well enough to calculate the exact affect that would have, but the length around the earth at the US’s latitude is not close to the same as the length around the earth at the equator (aka earth’s circumference).

All that is to say, I think the continental US should have 4 time zones because the length around the earth at our latitude is not 25,000 miles