# 24-hour clock

**URL:** <https://boards.straightdope.com/t/24-hour-clock/417821>\
**Category:** Miscellaneous and Personal Stuff I Must Share\
**Created:** [September 2, 2007, 5:57pm UTC](https://boards.straightdope.com/t/24-hour-clock/417821 "2007-09-02T17:57:29Z")\
**Posts on this page:** 3\
**Page:** 2

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**Author:** ![DudleyGarrett](https://avatars.discourse-cdn.com/v4/letter/d/d9b06d/32.png) [@DudleyGarrett](https://boards.straightdope.com/u/DudleyGarrett)\
**Post date:** [September 3, 2007, 1:21pm UTC](https://boards.straightdope.com/t/24-hour-clock/417821/21 "2007-09-03T13:21:22Z")

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[QUOTE=Tripler]  
Actually, it’s either way, depending on the activity and it’s duration. . .

If the mess hall is open from 2000 until 2400 on Wednesday, it’s open Wednesday night from 8:PM to 12:AM. If it’s open for breakfast at 0000 to 0400, it’s open from 12:AM to 4:AM in the morning.

It’s all a matter of context, but it’s sometimes done for ease of math (when figuring out durations) or just to make a point.

Tripler  
And if you’re eating breakfast that early, I am truly sorry.  
[/QUOTE]

Midnight meal, baby! A 1AM meal isn’t breakfast, it’s drunk food! Praise the chow hall for being open at that time!

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**Author:** ![A.R.Cane](https://avatars.discourse-cdn.com/v4/letter/a/ee7513/32.png) [@A.R.Cane](https://boards.straightdope.com/u/A.R.Cane)\
**Post date:** [September 3, 2007, 3:16pm UTC](https://boards.straightdope.com/t/24-hour-clock/417821/22 "2007-09-03T15:16:22Z")

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24:00 is used in military log books because they are normally kept to the minute, not the second. Often the change of day is logged to make it easier to find dates when rereading the log. So the typical entry might be 00:01 (date) a new day, or something to that effect.

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**Author:** ![Colophon](https://avatars.discourse-cdn.com/v4/letter/c/f05b48/32.png) [@Colophon](https://boards.straightdope.com/u/Colophon)\
**Post date:** [September 4, 2007, 12:47am UTC](https://boards.straightdope.com/t/24-hour-clock/417821/23 "2007-09-04T00:47:03Z")

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[QUOTE=Rayne Man]  
I have heard that a few years ago some computers could not cope with the concept of midnight expressed as 00.00.00. As an example this caused problems to a cross-channel ferry operator who had a scheduled sailing at midnight and to those people who wanted to book a ticket electronically. To get round this the actual advertised time for this boat was 23.59.00  
[/QUOTE]

Part of the reason might also be that if you advertise a boat as being at, say, 00:00 on Wednesday, you might get people turning up on Wednesday night, i.e. nearly 24 hours late.

Saying it is 23:59 on _Tuesday_ instead removes the ambiguity.

It’s the same reason that competition closing dates are often given as “11.59pm on August 31” or whatever. Some say “midnight on \<date\>” but I always think that’s ambiguous – I would _assume_ it meant the end of that given day, but then 00:00 is shown on clocks as being part of the _next_ day, as mentioned above. (But that is simply because if a clock shows “00:00:00” then by definition it is _after_ midnight, as the display doesn’t tick over until the exact moment passes.)

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