# 24-Hour Time (HH:MM)

Key: `datetime.time.hm_24h`

Hours and minutes only, no seconds. Common in schedules, timetables, and user-facing applications.

Page: <https://meridian.online/docs/projects/finetype/types/datetime/time/hm_24h>

Format: `%H:%M`

Samples: `10:30`, `23:59`, `00:00`

## Background

### Origin

On the 24-hour clock, a time of day is written in the form hh:mm, for example 01:23.[[1]](https://en.wikipedia.org/wiki/24-hour_clock) The colon is the most commonly used separator between hours, minutes and seconds on the 24-hour clock.[[1]](https://en.wikipedia.org/wiki/24-hour_clock) On the 24-hour clock, a leading zero is added for numbers under 10, but it is optional for the hours.[[1]](https://en.wikipedia.org/wiki/24-hour_clock)

The first edition of the ISO 8601 standard was published as ISO 8601:1988 in June 1988.[[2]](https://en.wikipedia.org/wiki/ISO_8601) ISO 8601 lets the seconds be omitted for brevity at the cost of precision, giving T\[hh\]:\[mm\] in the extended format.[[2]](https://en.wikipedia.org/wiki/ISO_8601) RFC 3339 defines partial-time as a two-digit hour, a colon, a two-digit minute, a colon and a two-digit second.[[3]](https://www.rfc-editor.org/rfc/rfc3339)

### Use

The value of an HTML time input is always in 24-hour format with leading zeros, HH:mm, regardless of the input format shown to the user.[[4]](https://developer.mozilla.org/en-US/docs/Web/HTML/Reference/Elements/input/time) An HTML time input's step defaults to 60 seconds, and with that default most browser time controls show hours and minutes but not seconds.[[4]](https://developer.mozilla.org/en-US/docs/Web/HTML/Reference/Elements/input/time) A web form's time input is submitted as name=HH%3Amm, or name=HH%3Amm%3Ass if seconds are included.[[4]](https://developer.mozilla.org/en-US/docs/Web/HTML/Reference/Elements/input/time)

OpenStreetMap's opening\_hours key writes hours as a 2-digit number in 24-hour format, with no am/pm, and minutes as a 2-digit number.[[5]](https://wiki.openstreetmap.org/wiki/Key:opening_hours) OpenStreetMap's opening\_hours syntax allows extended hours past midnight, so Mo 20:00-26:00 means open Monday from 20:00 until 2:00 the next morning.[[5]](https://wiki.openstreetmap.org/wiki/Key:opening_hours) The GTFS transit feed specification writes times as HH:MM:SS and records times after midnight on the service day as values greater than 24:00:00.[[6]](https://gtfs.org/documentation/schedule/reference/) Some bus and train timetables show 00:00 as a departure time and 24:00 as an arrival time.[[1]](https://en.wikipedia.org/wiki/24-hour_clock)

Style guides and military communication regulations in some English-speaking countries discourage 24:00 and recommend times near midnight be reported as 23:59 or 00:01 instead.[[1]](https://en.wikipedia.org/wiki/24-hour_clock) In the past, some European countries used the dot on the line as the separator in 24-hour times.[[1]](https://en.wikipedia.org/wiki/24-hour_clock) A value like 10.30 in an older European file may be a time of day rather than a decimal, so read the column header and neighbouring values before treating it as a number. (Meridian's view)

## Sources

1. [24-hour clock](https://en.wikipedia.org/wiki/24-hour_clock) — secondary source
2. [ISO 8601](https://en.wikipedia.org/wiki/ISO_8601) — secondary source
3. [RFC 3339: Date and Time on the Internet: Timestamps](https://www.rfc-editor.org/rfc/rfc3339) — standard
4. [\<input type="time"\> HTML attribute value - HTML \| MDN](https://developer.mozilla.org/en-US/docs/Web/HTML/Reference/Elements/input/time) — documentation
5. [Key:opening\_hours](https://wiki.openstreetmap.org/wiki/Key:opening_hours) — documentation
6. [Reference - General Transit Feed Specification](https://gtfs.org/documentation/schedule/reference/) — documentation