[verve_rat]

Um, add in a daylight savings transition and that "date" could be 23 or 25 hours long.

And that is not even getting into what a day means when you are trying to coordinate between NZ and the UK.

[Izkata]

To really get confusing, let's add in leap seconds. They're added "as needed" and it looks like our most recent one was in 2016.

https://en.wikipedia.org/wiki/Leap_second

[AprilArcus]

Good point! ISO 8601 dates should support timezones. Then a 24-hour "date" could only be in one of standard time or daylight time.