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This may seem like a duplicate but I didn't find the exact answer to this, and all related answers were opposite to each other and confusing to me.

At my work (in the US) we use 24-hour format. I usually write it e.g. '1735 hours' or '17:35' (without 'hours'). I usually get corrected by supervision to '17:35 hours'. In my understanding, it should be either no colon, but 'hours', either colon, no 'hours'. Not both. Is there an exact rule I can relay to?

  • You can have a look at ISO 8601. – Massimo Ortolano Apr 18 '17 at 19:40
  • This is not really a question about English, but about formatting. Your editor or style manual has the final say here. – choster Apr 19 '17 at 16:38
  • The simple answer is "Nope!" – Hot Licks Jan 9 '18 at 1:12
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There is nothing I can find that specially addresses the OP's question about using 16:30 versus 1630 hours in the many organizations that use a 24-hour time for communications and records; they seem to adopt whatever conventions or portions thereof are useful to their own organizations for avoiding ambiguity, which is the purpose. Nor is there anything that says that "16:30 hours" would be incorrect.

Many organizations use a 24-hour clock, adapting it to suit their own needs for avoiding ambiguity. U.S. military time is an adaptation of 24-hour universal time. The U.S. military's rules have been worked out with allies, especially English-speaking allies (agreed to, in AmE; agreed, in BrE) for clarity and to avoid confusion. Here's a bit from an article on saying it and writing it: How to Tell Time Like a Soldier.

0001 (12:01am): “zero zero zero one”
0215 (2:15am): “zero two fifteen”
1545 (3:45pm): “fifteen forty-five”

While saying “oh” for “zero” (“Be there at ‘oh six hundred!'”) is colloquial and often seen in movies and TV, saying “zero” is a part of military communication protocol.

As far as whether you should say “hours” after giving the time, that somewhat varies by what branch of the military you’re dealing with. If Soldiers and Airmen are saying 2:00pm, they’re a little more likely to give it to you as “fourteen hundred hours,” while Marines or Coast Guardsman are a little more likely to render it just “fourteen hundred.” Across the branches though, it’s typical to drop the “hours” bit when you’re talking face-to-face and your meaning is obvious, only adding it in conversation and written communication that’s more formal and where you want to make sure the message is clear.

Also, each time zone has a letter designation. U.S. East Coast time is R. List of military time zones (Wikipedia).

The letter J ("Juliet"), originally skipped, may now be used to indicate the observer's local time.[3] This is not an international standard, and many locations/fields may not recognize such use.

The letter Z ("Zulu") indicates Greenwich Mean Time (GMT) or Coordinated Universal Time (see UTC±00:00).

They are used in conjunction with military time: for instance, 6:00 a.m. in zone UTC−5 is written "0600R" and spoken "zero six hundred Romeo".

http://www.spacearchive.info/military.htm

Writing Military Time

Different professions and types of organizations write military time differently. The military, emergency services and hospitals usually write military time as hours and minutes without a colon and often add the word "hours" afterward.

Allied Communications Publication 121

This is a publication of the Combined Communications Electronics Board titled Allied Communications Publication 121 (October 2010). The CCEB is an organization created by the United States, the United Kingdom, Canada, Australia, and New Zealand. This publication is the only official one I've been able to find; its publications are compliant with NATO standards. It discusses the DTG (date-time group) in messages:

EXAMPLE: ø9163øZ JUL 11 represents 163ø GMT on 9th July 2ø11.

This is the way messages that arrive in the Situation Room at the U.S. White House are identified. I personally have done research in presidential libraries and seen a lot of messages with this DTG.

  • This isn't really related to the question, but I've occasionally wondered if there are any conventional pronunciations of military time that avoid the illogical use of "hundred (hours)" to refer to times exactly on the hour. – sumelic Apr 15 '17 at 19:12
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    According to Wikipedia: Hours are always "hundred", never "thousand"; 1000 is "ten hundred" not "one thousand"; 2000 is "twenty hundred". en.wikipedia.org/wiki/24-hour_clock#Military_time (probably a better source than the one I used above). Tradition trumps logic. – Xanne Apr 15 '17 at 19:17
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    "Ten hundred hours" is less ridiculous than "a thousand hours" would be, but both seem ridiculous to me. The day does not contain hundreds of hours. – sumelic Apr 15 '17 at 19:18
  • -1 no source you cite is authoritative – AmE speaker Apr 16 '17 at 14:01
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    With all due respect, this in not answering my question, I'm not in the military but in an agency which is using 24-hour format. And I'm aware how it's scripted and pronounced in the military. Just wondering if there is a format that allows both - the colon delimiters and the 'hours'. – Al Crow Apr 16 '17 at 21:20
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For a practical example, try the London Stock Exchange, Prices and Trades. Here's a sample from today's Associated British Foods (ABF):

Time/Date               Price       Currency    Volume    Trade Value

17:13:48 08-Jan-2018    2,854.94    GBX           306        8,736.12       
17:13:48 08-Jan-2018    2,872.97    GBX         4,403      126,497.00   

Financial websites make good examples, since they typically have to display tables with accurate times and multiple columns of data. They accomplish this by using the lowest acceptable precision (in this case seconds) and the smallest number of separators.

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I think it's a matter of semantic logic. 17:35 alone can be interpreted in a lot of ways, such as 17 minutes and 35 seconds, or 17 hours and 35 minutes. I would think that for this reason alone, putting the word hours makes it clear that you're talking about 17 hours and 35 minutes, and since the context is what time it is, it then becomes unambiguous that the time as 17:35 hours refers not to XX(00? 01? etc):17:35 but to 17:35:XX (seconds not important)

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