Timezones! Actual jurisdictional timezones, as in tzdata’s Europe/Lisbon! Hooray!
But humans do understand what a city is, and if they live in or near one they understand what the time is in that city, adjusting for any weird local political rules like "Daylight saving" because those rules affect their life.
It's the right granularity practically too. Can politicians decide that Dublin and Belfast are in different timezones? Yeah, it'd be difficult but I think they could make that happen. How about Queens and Brooklyn? Ahahaha No. The residents will defy any pretence that clocks change between one city block and the next, it would never stick.
Going from the example of "Europe/Lisbon", Valença and Tui have 1h of difference, but are located on the same longitude, <3km from one another...
- https://en.wikipedia.org/wiki/Valen%C3%A7a,_Portugal - https://en.wikipedia.org/wiki/Tui,_Pontevedra
Take Indiana. Indiana is in the US Eastern time zone, except for some places near the Illinois border, which are US Central. But Indiana also didn't observe DST until 2006 (although some counties did observe DST). Consequently, what could generally be described as three timezones (as in the MS timezone selector) is actually described as 11 timezones: https://en.wikipedia.org/wiki/Time_in_Indiana#tz_database
From what I understand, locals in Indiana actually refer to time simply as Eastern or Central (with non-observance of DST meaning you shift from Eastern in winter to Central in summer).
Years ago we visited my wife's family in Columbus with some frequency, once we visited the Wal-Mart supercenter in Phenix City (yes, it's spelled way wrong) Alabama, which is right on the eastern border of Alabama, also next to the river. Since I worked in Wal-Mart Information Systems at the time, I had quite a bit of access and noted that the store's systems were on Eastern time, even though the entire state of Alabama is on Central.
Sure enough: https://en.wikipedia.org/wiki/Phenix_City,_Alabama "Phenix City lies immediately west across the Chattahoochee River from the much larger Columbus, Georgia and observes Eastern Time on a de facto basis (in contrast to the rest of Alabama, which observes Central Time) due to Phenix City's strong economic ties to Columbus."
The Olson Database is amazing; I've non-trivially interacted with it a number of times in my career.
Even so, the final, on the ground authority is the people who use and are affected by time zones.
I found the Pendulum library [0] very intuitive when it comes to working with time. It makes it easy to do the right thing. For example, if you call `pendulum.now` it gives you a timestamp including your local timezone information. In other words, it preserves "the time on the clock on the wall", which is lost if you do what so many people do and just take UTC timestamps.
pendulum.now()
# DateTime(2020, 5, 28, 13, 32, 1, 303100, tzinfo=Timezone('Europe/London'))