Title should involve "US/*", not just "US".

> Let PDT be PDT(-8) and PST be PST(-7). Why do I need to choose Cupertino, CA (or LA in the blog post example)

Whether daylight savings time is being used at a given location at a given time of year is a matter of government policy. The city-based timezone selectors should handle that automatically based on the jurisdiction you choose.

> Sure, it's duplicate data but a backend system (Postgres config files, say) should only store the value of the TZ, i.e. -7 / -8.

Then the time may be wrong for half the year depending on where you are.

You can't just go by time zone names because there are weird exceptions, like most of Arizona not doing DST. Then there's Indiana, which didn't do DST until 20 years ago, and there are some counties that switched time zones when the DST law took effect... if you're in one of those counties will you just accept old timestamps being an hour off? Granted, this gradually becomes less of an issue the further we get from the change. But nothing guarantees that there won't be further changes in the future.

And that's just the US, there's almost 200 other countries each with their own laws.

A bit of an edge case, but there's also the problem that the time zone you pick today might not be the time zone you have tomorrow: The jurisdiction you're in can change what their clocks use on an institutional whim.

It's very unlikely, but tomorrow some state or major city in PST could decide to add 15 minutes to all their wall clocks. Should your computer's clock change? That depends on what you're using it for...

I suspect a large number of users might choose PST if in California, when they really mean PST/PDT. Or perhaps in the summer they would semi-correctly choose PDT.

Choosing a large city you know shares your time zone does make things a bit more “human“.

Even abbreviations have issues. PST (UTC+8) is also Philippine Standard Time. EST could mean Eastern Standard Time in Australia, granted that nowadays is AEST.

Timezones are such a headache. Obviously even UTC for a location varies depending on the time of year.

Even the International Space Station shifted timezones from Houston time to UTC+0.

Curiosity and Perseverance's clocks are UTC but operations run on LMST (local mean solar time) Gale Crater and LMST Jezero Crater- their landing locations. That point is moot until humans start spinning up VMs on Mars which they will one day.

> Let PDT be PDT(-8) and PST be PST(-7)

The problem is both the US and Australia have “EST/EDT” - the Australian version sometimes has an A stuck on the front to disambiguate it from the US timezone, but that isn’t always done (especially given some systems insist timezone abbreviations can be max 3 characters). And the problem with disambiguating on the basis of UTC offsets is you’d be surprised by how many people have no clue what any of them are. But “Americas” vs “Australia”, they’ll get that right

Offset alone is not enough because different TZ names also point to different DST schedules (current and historic) and past changes.

You can look at the tz data files to see what that looks like.

I'm curious as to what people in Phoenix would select as their timezone under your proposed solution?

if one is serious, one just chooses UTC.

one can play with timezones all they want, but in the end it's a presentation issue.