[eyelidlessness]

Another mistake I’ve seen is using one timezone code used interchangeably with others in the “same” timezone. This is bad because different locales have different DST rules, and because they have different governing authorities which can and do change the rules.

And another still: assuming that all of a state uses the same TZ. Quite a few do not! Arizona for instance has several tribal timezones which honor DST while the state does not. Nevada has a little sliver of mountain time. Michigan has four counties in central time. And so on.

This stuff is hard to get right. And it’s important. “Just use UTC” is often the naive solution but it’s not good enough for a variety of use cases.