ZD and LU: While “standard time” is a “modern day” invention, there were always two type of hours. The first, 12 “hours” of daylight and 12 hours of “night” commonly known as “shaah zmanios” which is used for halachic times such as Krias Shemah and Sof Zman Tefilla. In addition the chachomim understood that there were 24 hours, each hour consisting of 1080 Chalakim. This is how they calculated that each month is exactly 29 days, 12 hours, and 793 Chalakim.
The Shaah Zmanios doesnt work for modern societies because Halachic Noon is differnet in NYC than it is a Philadelphia and things like trains need to have a standard time so noon means the same thing in NYC and Philadephia so there is no confusion
Its not a big deal if the time for Shabbos is slightly differnet for both cities, but it is a big deal if a train is supposed to arrive at noon, you need to know what noon means
Chatzos will vary significantly across the whole time zone. But in any place it will not change significantly.
But noon changes by every time zone by an hour.
Your issue was that someone could not be consistent with “noon’ in a specific area, because you were considered about a train schedule. Which would be a specific place.
The train schedule is why standard time was created, but there are other reasons
People have conference calls all the time. And they the call is schedualed for Noon Eastern Time. You need to be exact to know what Noon eastern time is.
Halachic Noon is different in Los Angeles than it is in NY