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Comment by daedalus2027 | Hacker News Reader

daedalus2027

I saw when i was in Japan a various billboards marking a 25 hour service I thought it was some kind of mistake but apparently they call 1 am the hour 25...I think I saw it in Okinawa

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It’s more than just 25, they often go to 29, to indicate 5am. They do this to make it clear that it is an overnight service starting in one calendar day and terminating in another. It’s not just a simple substitute for “1 am”.

Actually it is pretty elegant system. Bit strange and extra calculation, but rather elegant option to pick.

You occasionally see times like 24:15 on European railway timetables. If the train runs only on weekdays, it might make it clearer that there isn't one at 00:15 on Monday.

I haven't noticed 25:00, but I don't often look at printed/PDF timetables nowadays.

I don't get it.

I think:

If a coffee shop opens at 5am, they say that. They never say 29.

If a bar stays open UNTIL 5am, they say 29.

Yep, and this makes it clear that they are NOT open Sunday because Saturday closes at 29 and there are no hours listed for Sunday.

Your flight leaves at 23 and arrives at 26. (11 PM to 2 AM next day)

Your return flight leaves at 2 and arrives at 11. (2 AM to 11 AM that same day)

Surprisingly, I like that as an informal system

Back when I was a night owl, I considered “today” to last until about 5am when you start hearing birds outside. Aligning semantic days with your schedule is incredibly convenient.

Now that I’m a morning person, the same concept of 5am semantic days still works perfectly. The day begins about 20min before my alarm.

Japanese VCRs could be programmed with times like 24/25/26/27:xx, which makes a lot of sense for TV programs that are part of “today’s” schedule but after midnight. Much lower risk of getting the day wrong when programming.

I've seen this when working on a side project involving public transport timetables from Google Transit. A service can run on 26:00 on Sunday, to indicate that the Sunday service is running 2 hours past midnight (i.e. on Monday 02:00).

https://developers.google.com/transit/gtfs/reference#stop_ti...

It's called 30-hour clock.

This convention is also used by some TV ratings measurement organizations - a show ending Tue 02:00 will be recorded as Mon 26:00, since it logically belonged to the day that ended, not the one that started.

Indeed, the "tv day" stretches from 02:00:00 to 25:59:59, but you usually don't actually use wall time (or in this case, modified wall time), and instead measure instant time as "minutes after midnight" (MAM) or "seconds after midnight" (SAM), so it's just an integer.

In Japan, clubs will announce opening times like "Friday 22:00〜27:00" meaning 10PM to 3AM the following day

As far as I know, that's actually used, when something starts in the "old" day and continues into the "new" day.

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