Time isn't different. Humans created labels that have been adhered to that's all.

If you left London and sailed to New York at 15 knots. It would take the same amount of time regardless of the standards in use.

That's not to say time is static, Einstein proved its relative, but that's a different consideration and one that has very little bearing on the conversation due to our relatively slow speeds.

When the speed of communication was faster than the rotation of the earth.

But what really made time zones a thing was trains. Everyone basically used their own local "highnoon" as a time reference and it wasn't working for keeping trains on a schedule

https://www.history.com/this-day-in-history/railroads-create-the-first-time-zones

It is the same time everywhere.

We just make up what time it is to make our lives easier. There is no particular reason that we need to use any specific time anywhere or all can't be on the same exact clock everywhere. We choose to do it because it can be useful.

Lets say we all agree that noon is when the sun is highest in the sky. No matter where you are, when the sun is highest, its noon. Of course noon in New York, is gonna be hours behind noon in London. This is how it works now, more or less.

But what if we didn't care where you were on earth?. What if noon was when the sun was highest in London, and everyone else used London time. For New York, the sun will be lower. But it would still be noon

Does any of it matter? Does it matter that the sun is lower in New York and its noon? Couldn't people in new york just say start their day at 1pm instead of 8am, then go to bed at like 3am?

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It's not literally "the same time everywhere."

In special relativity, simultaneity is relative and depends on your reference frame.

When it took months to cross an ocean no one really cared. Everyone just used their own local time. Most people didn't need to subdivide time that accurately. Sun comes up you work. Sun goes down work is done. Sun is at the highest point in the sky it's noon. The fact that the time wasn't the exact same as a town a several miles and hours away by foot (or horse) didn't matter.

Hipparcus proposed using the local time a lunar eclipse happened to calculate the longitude of a place. So, at least from Ancient Greece. I don't know how extended this knowledge was, though.

Finally a good answer!

if you're circumnavigating the globe, eventually you will care, at least a little bit.

A small bit of trivia that isn't worth a top-level comment: according to wikipedia, when Magellan's sailors returned from the first circumnavigation of the globe, they were off by a day and surprised by this.

(Also according to wikipedia, the loss/gain of a day by circumnavigators had been predicted a few hundred years earlier by Abulfeda, a geographer/historian/prince)

Excellent point about the importance of measuring time to determine longitude. Probably the main driver for more accurate time keeping during the Era of Exploration.

Before time zones, there was local time. Essentially, whenever the sun at its highest point in the sky is noon. This was particularly difficult for rail travel, because a town that is a few dozen miles away has a slightly different local time, and you can't set a train schedule unless everyone agrees what time is when. Trains also move fast enough that you can notice time zones. Horse and foot travel are too slow for this. The other big thing was the telegraph. With telegraphs, you can now communicate with people who are clearly experiencing a different time.

We've known that the Earth was round at least since Ancient Greece. And while they believed the Sun moved around the Earth, it still moved. Greeks were also really big into geometry and logic so they absolutely would have realized that when it's night on one side, it's day on the other.

If I were...idk, co-ordinating the use of assets stationed in Germany to bomb targets in Pakistan from an office in Virginia, I might have the whole operation on Zulu, sure.

Probably prehistory? If you see a big ball above your head starting on one side of the horizon and ending at the other side you can join the dots. If you climb a mountain at twilight you can see some places are lit up and some aren't.

Theologies at the time will have been very dependent on the passing heavenly bodies. Survival was very dependent on keeping the mind occupied, but the body at rest. Looking up and wondering was very important.

Considering that the time difference is the basis for knowing your longitude, navigators knew it a long time.

The average person in a village on the other hand, well there are people who have difficulty wrapping their heads around time zones today.

Actually crossing oceans meant you had to understand the time was different everywhere. Once Harrison came up with a clock that could keep accurate enough time so a mariner knew what time it was back at the prime meridian, mariners could determine their longitude.