Falsehoods programmers believe about time

When the timezone changes for daylight savings time, you either lose or gain 1 hour in that day (or whatever your local equivalent is).

well basically it's shorthand for "things that do not apply to every locale for X of instance of Y, that programmers have decided to implement as if they do apply to every locale or instance either through not realizing they do not apply or that the non-applicability in some situations are such bizarre outliers in relation to the rest of the world that it has been decided to be an acceptable bug that they will not fix" but that's not very pithy.

But of course what happens is the outliers have to deal with these systems that treat them as bad data possessing impossible properties and then the curse and say hey these stupid programmers don't realize that the world is not just like X1 or Y1, but that us rare instances of X2 and Y2 also exist!

And then an expert with sufficient knowledge about all the outliers compiles a list entitled Falsehoods Programmers believe about {X}.

I've worked with calendar applications and todo managers, alarms, recurring events and all that. Our timekeeping mechanics are incredibly complex.

24hs before 15:00 is USUALLY 15:00. But in some timezones, it can be (about once a year): 14:00, 16:00 or 14:59:59.

It's currently Monday 11:02 here, but it's likely still Sunday in some parts of the world (or is it already Tuesday somewhere? Not sure which is right). So, right now "today" have no single meaning; it depends on where you are.

Oh, and does your online meeting repeat at 14hs CET every Monday? Then for people in Argentina it will be at 9hs for six months a year, and at 10hs for another six months (due to CET having DST, but not Argentina).

September 1752

Programmer that have worked with timekeeping: yes.

Average programmer who hasn't done anything datetime-specific: unlikely.