Happy Leap Day

Someone has never had to coordinate a multi time zone meeting with IST.

Probably something to do with date arithmetic? For example, daylight saving time in Cuba begins at midnight on March 11th of this year, so:

import DateTime from "my-date-library";

let date = DateTime.date("2024-03-12", {
  timestamp: "00:00", 
  locale: "cuba/CU"
})/; // midnight the day after DST

date.subtract({ hours: 24 });

print(date.format("yyyy-MM-dd")); // "2024-3-10"
print(date.format("yyyy-MM-dd, hh:mm")); // "2024-3-10, 23:00"

We've just subtracted 24 hours, or 1 day. But we went back 2 days, because there were only 23 hours on March 11, not 24. Thus, "32 days" in March.

I haven't really thought about the semantics of writing a date library too much until now, but my guess is the right approach is to always calculate dates in absolute units from the beginning of time*", separately keep tabs on when DST is supposed to start in a given locale, and calculate the appropriate date representation based on whether or not it's DST.

I got the year wrong by 1 but 46 BC did have differemt length months in preparation for the introduction of the Julian calendar. That doesn't affect 46 BC in the Gregorian calendar, though.

Julius Caesar added Mercedonius (23 days) and two other intercalary months (33 and 34 days respectively) to the 355-day lunar year, to recalibrate the calendar in preparation for his calendar reform, which went into effect in 45 BC.[1][2][3] This year therefore had 445 days, and was nicknamed the annus confusionis ("year of confusion") and serves as the longest recorded calendar year in human history.[4] The actual planetary orbit-year remained the same.