How to Think About Time in Programming

(shanrauf.com)

189 points rmason | 1 comments | 24 Jun 25 20:01 UTC | HN request time: 0.248s | source

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Flundstrom2 ◴[24 Jun 25 21:16 UTC] No.44371152[source]▶

Time is a mess. Always. The author only scratched the surface on all the issues. Even if we exclude the time dilation of relativity which affects GPS/GNSS satellites - independent of if it is due to difference in gravitational pull or their relative speed over ground, it's still a mess.

Timezones; sure. But what about before timezones got into use? Or even halfway through - which timezone, considering Königsberg used CET when it was part of Germany, but switched to EET after it became Russian. There's even countries that have timezones differenting by 15 minutes.

And dont get me started on daylight savings time. There's been at least one instance where DST was - and was not - in use in Lebanon - at the same time! Good luck booking an appointment...

Not to mention the transition from Julian calendar to Gregorian, which took place over many, many years - different by different countries - as defined by the country borders at that time...

We've even had countries that forgot to insert a leap day in certain years, causing March 1 to occur on different days altogether for a couple of years.

Time is a mess. Is, and aways have been, and always will be.

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johnisgood ◴[25 Jun 25 06:39 UTC] No.44374234[source]▶

>>44371152 #

It is, there are a couple of timezones where not only there is a hour difference, but even a 30 and 45 minutes difference. India is UTC +5:30, and Lord Howe Island is UTC +10:30 / +11:00 and New Zealand, Chatham Islands is UTC +12:45 / +13:45, Iran is UTC +3:30 / +4:30 and so on. Where the format is X / Y, that means X is Standard Time, and Y is Daylight time.

Messy.

I think the full list can be found here: https://www.timeanddate.com/time/time-zones-interesting.html

You can use a Bash script that can give you an exhaustive list based on files from /usr/share/zoneinfo/, i.e. find timezones with non-whole hour offsets.

replies(1): >>44374288 #

volemo ◴[25 Jun 25 06:49 UTC] No.44374288[source]▶

>>44374234 #

I don’t understand this. What practical difference does it make making the time to round to the nearest quarter of an hour instead of the nearest hour? Personally, I don’t care if noon (sun is in zenith) happens half an hour before 12:00 or half an hour after.

Why do such time zones exist?

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1. johnisgood ◴[25 Jun 25 21:45 UTC] No.44382097[source]▶

>>44374288 #

Oh by the way, check this out, this is one of the news in 2025b tzdata:

  # From Roozbeh Pournader (2025-03-18):
  # ... the exact time of Iran's transition from +0400 to +0330 ... was Friday
  # 1357/8/19 AP=1978-11-10. Here's a newspaper clip from the Ettela'at
  # newspaper, dated 1357/8/14 AP=1978-11-05, translated from Persian
  # (at https://w.wiki/DUEY):
  # Following the government's decision about returning the official time
  # to the previous status, the spokesperson for the Ministry of Energy
  # announced today: At the hour 24 of Friday 19th of Aban (=1978-11-10),
  # the country's time will be pulled back half an hour.

From https://github.com/eggert/tz/blob/main/asia#L1503.

Pretty sure we can find a lot more oddities that are way worse.

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