Talk:12-hour clock

The existence of 24:00 or 2400

In a recent edit summary, JMF stated "24:00 is never used in 24-hour notation. Military uses 23:59 to prevent misunderstandings."

On 15 May 2025 the United States Department of the Air Force published a memorandum, DAFMAN11-401 Aviation Management. This memorandum uses 2400 on page 65. Jc3s5h (talk) 18:07, 26 August 2025 (UTC)

How standards have slipped! () 𝕁𝕄𝔽 (talk) 18:42, 26 August 2025 (UTC)

You sometimes need the actual midnight rather than minute before or after. Even ACP 121 which is used as a ref in this article used "2400" to refer to the midnight exactly. It said not to use 0000 and only to avoid 2400 "unless it is necessary to indicate this particular instant of time". – MwGamera (talk) 20:30, 26 August 2025 (UTC)

Hi, I'm an anonymous user who made an edit to the page in question. I was the one who added 24:00 (twenty-four o'clock) to the table, but I made a mistake because 24:00 (twenty-four o'clock) doesn't exist. In the 24-hour format, midnight is represented by 00:00 (zero o'clock). User JMF is correct about removing 24:00 (twenty-four o'clock) from the table.2804:214:8118:3D3A:B476:3D06:EF29:967 (talk) 00:08, 28 August 2025 (UTC) — Preceding unsigned comment added by 284:8118:3D3A:DDF7:71B9:95C7:965C (talk • contribs)

I don't have opinion regarding its inclusion in the table; inclusion seems likely to be more contentious than omission and it hardly matters in the article about 12-hour clock. But it really depends who you ask and according to which standard. Just like with am/pm at noon and midnight. Saying that 24:00 "doesn't exist" or that it's "never used" without any further qualification is simply false. Either is allowed in ISO 8601, for example. (@Jc3s5h: was there any edition that did not allow it?) Some profiles like that of W3C or RFC 3339 indeed limited it to allow only 00:00. But in military contexts, conversely, 2400 (twenty-four hundred) seems to be more common, at least in the past. Look at the sources under 24-hour clock § Midnight 00:00 and 24:00. If you follow, for example, ACP 121 or the older version of SECNAV M-5216.5 from before 2015, then it's 0000 that "doesn't exist". It's not a slip. – MwGamera (talk) 14:17, 28 August 2025 (UTC)

I conceded the point given that Jc3s5h cited the RS. But I am surprised. If an attack is to begin "at midnight on Sunday" or worse still "24:00 on Sunday" or "00:00 on Sunday", is that Saturday night/Sunday morning or Sunday night/Monday morning. 23:59 Sunday is unambiguous. Though I suspect a wise general would avoid it completely and choose for 04:00. So my "it doesn't exist" really means "I've never seen it" which is (a) OR and (b) evidence that anybody sensible steers well clear to avoid the confusion. 𝕁𝕄𝔽 (talk) 15:07, 28 August 2025 (UTC)

A more common example would be a change in a regulation that goes into effect on a certain date. Although the original regulation probably just specifies a date, the local commander may want to interpret it for his/her subordinates by including a time of day. The time of day might be 0000 local time, or perhaps 1900 local time the day before what is stated in the regulation if the regulation is controlled by UTC. Technically, the local commander might not have the authority to change the effective date & time by a minute. Jc3s5h (talk) 17:04, 28 August 2025 (UTC)

The difference between 24:00 and 00:00 is only relevant if you also include the date. Like
Every night at 00:00(or 24:00) the batchjob starts.
On the 21st of February at 00:00 (implying this as 21st starts)
2025 ends on 31st december 24:00

IM(notso)HO — Preceding unsigned comment added by 37.96.98.88 (talk) 10:23, 18 September 2025 (UTC)

Jc3s5h and JMF: I think it's better to make this clearer and not add 24:00 to the table, as readers might get confused and think the same day has two midnights. The day actually starts at 00:00 (12:00 am) and ends at 23:59 (11:59 pm). If 24:00 exists, how would it be converted to 12-hour format? 12:00 am is synonymous with 00:00. One minute after 23:59, it is 00:00 the next day. It makes no sense to say that 24:00 on December 31, 2025 is the same as 00:00 on January 1, 2026, since the 24:00 time slot does not exist. Just as there are no times where the minute is the number 60. I know that the 24-hour format works by adding 12 more in the hours from 1:00 pm to 11:59 pm, and in the case of midnight, it is different, as midnight is the beginning of the day, so the correct way is to restart the count, subtracting 12 by 12, which results in 0, that is, 00:00. Midnight (12:00 am or 00:00) is the first hour of the day, not the last. The last hour of the day is 23:00 (11:00 pm). If midnight were the last hour of the day, then it would make sense for it to be 24:00, if the day started at 01:00 (1:00 am). I know that on analog clocks in 24-hour format, it is possible to see the number 24 representing midnight and even so, this is incorrect, as the correct number is 0 (or 00) representing midnight on these analog clocks. As I said before, I was the one who put 24:00 in the table and I recognized my mistake. 24:00 does not exist. Just as days in number (1 to 31), days of the week (Sunday to Saturday), months (January to December) and years are the same for the entire planet Earth, so the schedules follow this same logic. So, rethink the inclusion of 24:00 in the table. The difference in time is that there are two formats, 12-hour (AM/PM) and 24-hour. If 12:00 am and 00:00 are the same time, what would 24:00 be in 12-hour format? 2804:5758:0:4AA4:EC63:C1F8:9A33:B726 (talk) 14:08, 18 September 2025 (UTC)

Jc3s5h and JMF: It's the same thing as me saying that 00:00 on January 1, 2026 is the same thing as 23:60 on December 31, 2025. Times with minutes represented by the number 60 do not exist, as I said before. 2804:5758:0:4AA4:EC63:C1F8:9A33:B726 (talk) 14:11, 18 September 2025 (UTC)

"...readers might get confused and think the same day has two midnights." Each day has two midnights, one at the beginning and one at the end. Only reliable sources matter, not the opinions of Wikipedia editors. Nobody believes declarations by Wikipedia editors that something doesn't exist. Jc3s5h (talk) 14:38, 18 September 2025 (UTC)

You are of course strictly correct. Nevertheless, Wikipedia reports what is actually used, not should be used. See also WP:righting great wrongs. 𝕁𝕄𝔽 (talk) 14:56, 18 September 2025 (UTC)

The table in the article is documenting what reliable sources say

The aim of the table is not to give the "correct" version: that is not for Wikipedia to say. The table in the article is documenting what wp:reliable sources say, even though they disagree. So edits to change it away from what the citations say must be reverted. See policy Wikipedia is not a publisher of original research. 𝕁𝕄𝔽 (talk) 00:07, 27 February 2026 (UTC)

Japanese usage

I removed this paragraph:

In Japanese usage, midnight is written as 午前0時 (0 a.m.) and noon is written as 午後0時 (0 p.m.), making the hours numbered sequentially from 0 to 11 in both halves of the day. Alternatively, noon may be written as 午前12時 (12 a.m.) and midnight at the end of the day as 午後12時 (12 p.m.), as opposed to 午前0時 (0 a.m.) for the start of the day, making the Japanese convention the opposite of the English usage of 12 a.m. and 12 p.m.[ref name="NAO Japan"]

The reference does not show that the Japanese version is the reverse of English, it shows that it is generally much less ambiguous (because you can write either "12 hours of the first half of the day (午前)" or "0 hours of the second half of the day (午後)". Anyway, this is not really relevant unless we want to have a comprehensive "12-hour clocks of the world" section. Imaginatorium (talk) 07:45, 2 March 2026 (UTC) Imaginatorium (talk) 07:45, 2 March 2026 (UTC)

Thanks, I agree with your decision. I disabled the ref because it won't work without the definition from the article. Johnuniq (talk) 09:13, 2 March 2026 (UTC)

My position

I'm not vandalizing. I don't understand why my edits aren't accepted, however, the table is very confusing; 24:00 doesn't exist, it would only exist if the civil day had 25 hours going from 00:00 to 24:59. The civil day only has one midnight. Regarding the names of the periods of the day, even though they are defined according to the position of the sun, I think the font used is valid. I know the table was shaped based on other cultures, but this can cause confusion here. Stating that the civil day begins at midnight and also at noon in the same table would indeed create confusion for readers. ~2026-15407-72 (talk) 21:45, 10 March 2026 (UTC)

Or you could put 24:00 in the table as the "ghost hour," because in digital clocks in 24-hour format, the countdown starts at 00:00 and ends at 23:59, and after 23:59 comes 00:00 of the next calendar day. ~2026-15407-72 (talk) 21:51, 10 March 2026 (UTC)

Or they could list 24:00 as a "civil day's game over" in the table, since they insist in keeping it there. ~2026-15407-72 (talk) 22:06, 10 March 2026 (UTC)

I know there are conventions in different countries, but that's already explained on the page. Leaving it in the table will confuse readers, and we know it's clear that 12:00 am is midnight and 12:00 pm is midday/noon. My goal is simply to avoid making the table confusing. ~2026-15354-13 (talk) 01:05, 11 March 2026 (UTC)

WP is not here to report "your view". See previous comments above. Note that good faith attempts to improve the page are never vandalism, but once you have been asked to stop, persisting becomes vandalism. Imaginatorium (talk) 02:46, 11 March 2026 (UTC)

@Imaginatorium: It does not become vandalism; see Wikipedia:Vandalism#Disruptive editing or stubbornness. Wikipedia:Disruptive editing is not the same as vandalism, which has a very specific meaning on the English Wikipedia. - Aoidh (talk) 11:18, 13 March 2026 (UTC)

The 6-hour clock

Sorry, I have no sources to hand, but I have seen at least two clocks, one inside the entrance to the cathedral of Prato, the other in Perugia, which have a single hand, which rotates four times a day. This doubles the apparent resolution of the time indication, so is adequate for ordinary timekeeping. It would be nice if someone can find references for this and add to the article. Imaginatorium (talk) 05:32, 23 June 2026 (UTC)