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Comment by jon-wood | Hacker News Reader

I grew up in the UK and still couldn’t tell you this off the top of my head. Most people can’t - when setting up systems with a cutoff date/time I’ve regularly been asked to have them expire at 11:59pm, because it avoids any ambiguity here.

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I think that's generally a sensible idea. Anything which required a schedule for humans to read - theatre performances, trains, planes, etc - are better off being scheduled for 23:55, 23:59, 00:01 or 00:05 than exactly at midnight because lots of people don't understand or get confused whether 00:00 on a date means the start or the end of the day.

I do enjoy though where systems have to deal with 'weird' days. I believe in the UK the rail ticketing system works on essentially a 26h day - that is to say if you buy a ticket at on 5th November, it will be valid until 04:00 on 6th November, so in some sense the hours 00:00-04:00 belong to both days.

I remember reading somewhere that some systems use a 26 hour clock in that it's literally valid 00:00 to 25:59, or 28 hr for 00:00 to 27:59. 24:30 10/1 and 00:30 11/1 mean the exact same thing, it's a notational convenience to not have to worry about date boundaries between days.

Trying to find the source again but not having success.

TV stations use this system. A schedule for any given day can be up to 27 hours iirc.

The Thomas Cook European Rail Timetable uses 00:00 for a train departing at midnight, and 24:00 for a train arriving at midnight.

> Most people can’t

Bias. Most people can. I'm in the UK, too.

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