Ask HN: Did you encounter any leap year bugs today?

There's often someone out there who interprets such things as a 3 month, or 1 year retention policy and that it means they're entitled to look at the entire range whenever they want.

Anyway, I'm not sure there's any more or less logical date to use and Feb 29th babies seem to choose both about equally:

> “I love when people ask me, ‘Do you celebrate on Feb. 28 or March 1?’” said Raenell Dawn, a co-founder of Honor Society of Leap Year Day Babies. “I get to tell them, ‘Both, because I can.’ But I’m a February baby; I was not born in March.” An informal poll of the society’s members showed about a 50-50 split between the two dates, said Ms. Dawn, who is celebrating her “Sweeter 16” by turning 64 this year.

https://www.nytimes.com/2024/02/28/style/leap-year-explained...

If you want to celebrate your birthday at the moment earth reaches the same spot around the sun as when you were born, then we’d all have the same issue - we’d have to celebrate it 6 hours later every year, reseting every 4 years.

February 29 is very much a new day… which simply doesn’t exist on non-leap years.

Correct.

> And Feb 29 + 730 days = Feb 27

Incorrect. It's Feb 28 again. In a normal, non-leap year, if you add 365 days then you get back to the same date.

As a surprise for a friend of mine, I threw him a gigasecond party on the day he turned 1000 million seconds old. Yes he was surprised, and a good time was had by all.

When I wrote "+ 1 year" I meant year to represent 365 or 365.25 days, not "the same day next year.":

  >>> from datetime import date, timedelta
  >>> year = timedelta(days=365.25)
  >>> date(2024, 2, 29) + year
  datetime.date(2025, 2, 28)

> Note that in the context of birthdays, people use "calendar years," not "unit of time which is ~1 revolution around the sun."

You've never heard someone say they've celebrated another trip around the Sun? I literally have a photo from 2007 of my daughter in Montessori celebrating her birthday by holding a globe and walking around a candle representing the Sun. I think most people probably don't really think about whether it's a calendar year or astronomical year because for most people, they are usually equivalent and it doesn't matter.

But that's all beside the point. All I meant to point out is that I disagree that March is more logical. I don't think logic points us to one month or the other. You may feel March is more logical, but I don't accept your priors, so for me March is not more logical than February.

Your calendar year birthday would be March 1 since one full calendar year has elapsed.

But Feb 28 is the nearest day to one full solar year, assuming you were born before about 6pm local time on Feb 29.

Two-day long birthday it is! :)

You should use a monotonic clock with an arbitrary starting point anyway, unless you need some kind of synchronization between devices, but you probably wouldn't use unixtime there anyway.

This is a fairly typical informal usage of the word correlation in my experience, and while it might not be _technically correct_ (I don't know, I'm not an expert), it's an often enough used idiom.