Editing 24-hour clock (section)

== Description ==
{| class="wikitable" style="float:right; margin:0.5em 0 0.5em 1em; font-size:95%;"
!24-hour clock||[[12-hour clock]]||Part of the day
|-
| 00:00||midnight{{Efn|name=noonmidnight}}<br />12:00&nbsp;a.m. || rowspan = 6 | Postmidnight<ref>https://www.merriam-webster.com/dictionary/postmidnight</ref><ref>https://www.collinsdictionary.com/dictionary/english/postmidnight</ref>
|-
| 01:00||1:00&nbsp;a.m.
|-
| 02:00||2:00&nbsp;a.m.
|-
| 03:00||3:00&nbsp;a.m.
|-
| 04:00||4:00&nbsp;a.m.
|-
| 05:00||5:00&nbsp;a.m.
|-
| 06:00||6:00&nbsp;a.m. || rowspan = 6 | [[Morning]]
|-
| 07:00||7:00&nbsp;a.m.
|-
| 08:00||8:00&nbsp;a.m.
|-
| 09:00||9:00&nbsp;a.m.
|-
| 10:00||10:00&nbsp;a.m.
|-
| 11:00||11:00&nbsp;a.m.
|-
| 12:00||midday<br>noon{{Efn|See: {{section link|12-hour clock|Confusion at noon and midnight}}|name=noonmidnight}}<br />12:00&nbsp;p.m. || rowspan = 6 | [[Afternoon]]
|-
| 13:00||1:00&nbsp;p.m.
|-
| 14:00||2:00&nbsp;p.m.
|-
| 15:00||3:00&nbsp;p.m.
|-
| 16:00||4:00&nbsp;p.m.
|-
| 17:00||5:00&nbsp;p.m.
|-
| 18:00||6:00&nbsp;p.m. || rowspan = 6 | [[Evening]] / [[night]]
|-
| 19:00||7:00&nbsp;p.m.
|-
| 20:00||8:00&nbsp;p.m.
|-
| 21:00||9:00&nbsp;p.m.
|-
| 22:00||10:00&nbsp;p.m.
|-
| 23:00||11:00&nbsp;p.m.
|-
| colspan="3"|{{notelist}}
|}
[[File:12 24 Hours World Map.svg|thumb|World map showing the usage of 12 or 24-hour clock in different countries{{legend|#f0027f|24-hour}}{{legend|#990052|24-hour (12-hour orally)}}{{legend|#7fc97f|Both in common use}}{{legend|#386cb0|12-hour (except in special circumstances such as [[aviation]])}}]]
[[File:World War II RAF sector clock.jpg|thumb|World War II RAF [[sector clock]] that can be read in 24-hour notation.]]
[[File:Digital clock in THSR Miaoli Station.jpg|thumb|24-hour digital clock in [[Miaoli HSR station]].]]
[[File:24 hour analog clock rua 24 horas curitiba brasil.jpg|thumb|A public 24-hour clock in [[Curitiba]], Brazil, with the hour hand on the outside and the minute hand on the inside.]]

A time of day is written in the 24-hour notation in the form hh:mm (for example 01:23) or hh:mm:ss (for example, 01:23:45), where hh (00 to 23) is the number of full hours that have passed since [[midnight]], mm (00 to 59) is the number of full minutes that have passed since the last full hour, and ss (00 to 59) is the number of seconds since the last full minute. To indicate the exact end of the day, hh may take the value 24, with mm and ss taking the value 00. In the case of a [[leap second]], the value of ss may extend to 60. A leading zero is added for numbers under 10, but it is optional for the hours. The leading zero is very commonly used in computer applications, and always used when a specification requires it (for example, [[ISO 8601]]).

Where subsecond resolution is required, the seconds can be a [[Decimal#Decimal fractions|decimal fraction]]; that is, the fractional part follows a decimal dot or comma, as in 01:23:45.678. The most commonly used separator symbol between hours, minutes and seconds is the [[colon (punctuation)|colon]], which is also the symbol used in ISO 8601. In the past, some European countries used the [[Full stop|dot on the line]] as a separator, but most national standards on time notation have since then been changed to the international standard colon. In some contexts (including some computer protocols and military time), no separator is used and times are written as, for example, "2359".

=== Midnight 00:00 and 24:00 ===
{{redirect|23:59|the Christian metal album|Veni Domine#Discography|the film|23:59 (film)}}
In the 24-hour time notation, the day begins at midnight, 00:00 or 0:00, and the last minute of the day begins at 23:59. Where convenient, the notation 24:00 may also be used to refer to midnight at the end of a given date<ref>{{cite ISO standard |title=ISO 8601:2004 – Data elements and interchange formats – Information interchange – Representation of dates and times |csnumber=40874 |edition=3rd |at=Clause 4.2.3 "Midnight" |date=2004}}</ref>&nbsp;— that is, 24:00 of one day is the same time as 00:00 of the following day.

The notation 24:00 mainly serves to refer to the exact end of a day in a time interval. A typical usage is giving opening hours ending at midnight (e.g. "00:00–24:00", "07:00–24:00"). Similarly, some bus and train timetables show 00:00 as departure time and 24:00 as arrival time. Legal contracts often run from the start date at 00:00 until the end date at 24:00.

While the 24-hour notation unambiguously distinguishes between midnight at the start (00:00) and end (24:00) of any given date, there is no commonly accepted distinction among users of the 12-hour notation. [[Style guide]]s and military communication regulations in some English-speaking countries discourage the use of 24:00 even in the 24-hour notation, and recommend reporting times near midnight as 23:59 or 00:01 instead.<ref name=acp121>{{cite book |url=http://jcs.dtic.mil/j6/cceb/acps/acp121/ACP121I.pdf |title=Communication instructions – General |id=ACP 121(I) |page=3{{hyp}}6 |publisher=Combined Communications-Electronics Board |date=October 2010 |archive-url=https://web.archive.org/web/20110807210103/http://jcs.dtic.mil/j6/cceb/acps/acp121/ACP121I.pdf |archive-date=7 August 2011}}</ref> Sometimes the use of 00:00 is also avoided.<ref name=acp121 /> In variance with this, an older version of the correspondence manual for the [[United States Navy]] and [[United States Marine Corps]] specified 0001 to 2400.<ref>{{cite book |url=http://www.marforres.marines.mil/Portals/116/Docs/G-1/AAU/AAUDocuments/CORRESPONDENCE%20MANUAL.pdf |id=SECNAV M-5216.5 |title=Department of the Navy Correspondence Manual |date=March 2010 |publisher=[[United States Department of the Navy]] |at=Chapter 2, Section 5 Paragraph 15. Expressing Military Time}}</ref> The manual was updated in June 2015 to use 0000 to 2359.<ref>{{Cite book |url=https://www.marines.mil/Portals/59/Publications/SECNAV%20M%205216.5.pdf |id=SECNAV M-5216.5 |title=Department of the Navy Correspondence Manual |date=June 2015 |publisher=[[United States Department of the Navy]] |at=Chapter 2, Section 5 Paragraph 15. Expressing Military Time}}</ref>

=== Times after 24:00 ===
{{See also|Date and time notation in Japan#Time}}
Time-of-day notations beyond 24:00 (such as 24:01 or 25:00 instead of 00:01 or 01:00) are not commonly used and not covered by the relevant standards. However, they have been used occasionally in some special contexts in the United Kingdom, France, Spain, Canada, Japan, South Korea, Hong Kong, and China where business hours extend beyond midnight, such as broadcast television production and scheduling. The [[General Transit Feed Specification|GTFS]] public transport schedule listings file format has the concept of service days and expects times beyond 24:00 for trips that run after midnight.<ref>{{Cite web|url=https://developers.google.com/transit/gtfs/reference|title=Reference &#124; Static Transit|website=Google Developers}}</ref>

=== Computer support ===
In most countries, computers by default show the time in 24-hour notation. For example, [[Microsoft Windows]] and [[macOS]] activate the 12-hour notation by default only if a computer is in a handful of specific language and region settings. The 24-hour system is commonly used in text-based interfaces. [[POSIX]] programs such as [[ls]] default to displaying timestamps in 24-hour format.

=== Military time ===
[[File:24-Hour Clock Aboard the USS Midway (8727193240).jpg|thumb|24-hour clock as seen on the [[USS Midway (CV-41)|USS Midway]].]]
In [[American English]], the term ''military time'' is a synonym for the 24-hour clock.<ref>{{Cite encyclopedia |url=http://www.lexico.com/definition/military_time |archive-url=https://web.archive.org/web/20201112033709/https://www.lexico.com/definition/military_time |url-status=dead |archive-date=12 November 2020 |title=military time |dictionary=[[Lexico]] UK English Dictionary |publisher=[[Oxford University Press]]}}</ref> In the US, the time of day is customarily given almost exclusively using the 12-hour clock notation, which counts the hours of the day as 12, 1, ..., 11 with suffixes ''a.m.'' and ''p.m.'' distinguishing the two [[Day|diurnal]] repetitions of this sequence. The 24-hour clock is commonly used there only in some specialist areas (military, aviation, navigation, tourism, meteorology, astronomy, computing, logistics, emergency services, hospitals), where the [[12-hour clock#Confusion at noon and midnight|ambiguities of the 12-hour notation]] are deemed too inconvenient, cumbersome, or dangerous.

Military usage, as agreed between the United States and allied English-speaking military forces,<ref>{{Cite web
| title=Communication Instructions General ACP 121(I)
| url=http://jcs.dtic.mil/j6/cceb/acps/acp121/ACP121I.pdf
| url-status=dead
| archive-url=https://web.archive.org/web/20160508202743/http://jcs.dtic.mil/j6/cceb/acps/acp121/ACP121I.pdf
| archive-date=8 May 2016
}}</ref> differs in some respects from other twenty-four-hour time systems:
*No hours/minutes separator is used when writing the time, and a [[Nautical time#Letter suffixes|letter designating the time zone]] is appended (for example "0340Z").
*[[Leading zero]]s are always written out and are required to be spoken, so 5:43&nbsp;a.m. is spoken "zero five forty-three" (casually) or "zero five four three" (military radio), as opposed to "five forty-three" or "five four three".
*[[List of military time zones|Military time zones]] are lettered and given word designations from the [[NATO phonetic alphabet]]. For example, in [[Eastern Time Zone|US Eastern Standard Time]] (UTC−5), which is designated time zone R, 2:00&nbsp;a.m. is written "0200R" and spoken "zero two hundred Romeo".
*Local time is designated as zone J or "[[NATO phonetic alphabet|Juliett]]". "1200J" ("twelve hundred Juliett") is noon local time.
*[[Greenwich Mean Time]] (GMT) or [[Coordinated Universal Time]] (UTC) is designated time zone Z, and thus called "Zulu time". (When used as a modern time zone, in practice, GMT and UTC coincide. For other purposes there may be a difference of about a second.<ref>{{Cite journal| last1 = Guinot| first1 = Bernard | date = August 2011 | volume=48 | issue=4 | title = Solar time, legal time, time in use | journal = Metrologia | page =185 | doi = 10.1088/0026-1394/48/4/S08|bibcode = 2011Metro..48S.181G| s2cid = 121852011 }}</ref>)
*Hours are always "hundred", never "thousand"; 1000 is "ten hundred" not "one thousand"; 2000 is "twenty hundred" not "two thousand".