Timezones are artificial constructs that people have made up, that is why they are just a line you cross.

If you move from one country to the next you suddenly are subject to all sorts of different man made laws and sometimes even manmade ideas of what time it is.

Because that is all timezones are a government declaring what time it is inside their borders.

Timezones are artificial but they are based on a natural things that is more real.

You know how the sun rises in the east and sets in the west?

If you move westwards you experience dawn and noon and sunset slightly earlier than someone east of you. (Like seeing a cars headlights sooner if you are further in the direction it is coming from.)

when we first came up with ways to tell the time we were pretty simple about it we had dawn and dusk when the sun rises and sets and we had midnight in the middle of the night halfway between sunset and dawn and noon halfway between dawn and dusk.

You didn't need a clock to tell the time just your eyes.

Dawn was at a slightly different time everywhere, but people would have to travel quite a bit to notice the difference and they traveled so slow that nobody really felt the difference.

Later people separated the time when the sun was up into 12 equal part called hours and the time when in wasn't into another 12 hours.

This mean that how long an hour was differed from day to day and location to location , but it was just a convenient way to split up the time between dawn and noon into 6 parts and so on.

Later the whole day night cycle was split into 24 equal parts this meant that dawn did always happen at the same hour but all hours were the same length.

than at some point when timekepeing got good enough we split the hour into 60 minute parts and got minutes and later still split those into 60 second minute part and got seconds.

At that point we basically had the time we have today.

The difference being that each place had its own time.

Noon was always halfway between dawn and dusk when the sun was highest in the sky.

Each town with it own church tower clock had its own local time based on the sun.

If you were rich enough to have an accurate clock or watch and set it based on the official time in one town and then traveled east or west to another town your clock would be off.

Of course clocks weren't very accurate or and travel was slow for most people.

The invention of a very accurate clock that could be compared to the time as seen from the sun was actually what enabled sailors to tell how far west or east they had travailed and thus tell where they were.

This all was very well until railroads came along.

Steam engines can move people very fast over great distances, fast enough that the time difference between towns mattered.

Keeping an accurate schedule is very hard when each town you stop has its own timezone.

Railroad companies made things easier by creating a unified time for their company.

At first this made things more complicated because each company decided on a different time, so you essentially could move between timezones by going from one platform to the next.

Eventually this shook out to the system we have today though were each country or in large countries each state within the country chooses a timezone based roughly on what the time would be based on the sun somewhere nearby. These timezones are mostly offset from each other by a full hour with a few exception being 30 or 15 minutes of.

These timezones are mostly the same north and south of where you are and different if you go far enough east or west.

In a few place you can go to a different timezone by going north or south though.

Noon and midnight will always happen simultaneously in a single line north to south from pole to pole (ignoring midnight sun phenomena etc) The line of when dawn and dusk happens is not quite north south but somewhat angled at times. So it can happen sooner or later north and south of you.

The legal time however isn't bound by that natural time. it follow the lines drawn by man

La of California has the same timezone, but if you go from Baja California to Baja California South in Mexico you move between timezone even if the dividing line between the two states is east to west.