Date and time notation by country

Different conventions exist around the world for date and time representation, both written and spoken.

Differences can exist in:

International standard ISO 8601 (Representation of dates and times) defines unambiguous written all-numeric big-endian formats for dates, such as 1999-12-31 for 31 December 1999, and time, such as 23:59:58 for 23 hours, 59 minutes, and 58 seconds.

These standard notations have been adopted by many countries as a national standard, e.g., BS EN 28601 in the UK and similarly in other EU countries, ANSI INCITS 30-1997 (R2008), and FIPS PUB 4-2 in the United States (FIPS PUB 4-2 withdrawn in United States 2008-09-02). They are, in particular, increasingly widely used in computer applications, since the most to least significant digit order provides a simple method to order and sort time readings.

Many countries use the ISO YYYY-MM-DD date format generally, and they have the advantage of being unambiguous. (YYYY means four-digit year, MM means two-digit month, and DD means two-digit day.) Local conventions can vary, and for the commonly used Gregorian calendar & Julian calendar sometimes include formats like DD-MM-YYYY, MM-DD-YYYY, YYYY-MM-DD, or even with the month written in Roman numerals. Dates can also be written out partly or completely in words in the local language.

The 24-hour clock enjoys broad everyday usage in most non-English speaking countries, at least when time is written or displayed. In some regions, for example where German, French and Romanian are spoken, the 24-hour clock is used today even when speaking casually, while in other countries the 12-hour clock is used more often in spoken form.

In most English-speaking regions, particularly the United States and the Commonwealth, the 12-hour clock is the predominant form of stating the time, with the 24-hour clock used in contexts where unambiguity and accurate timekeeping are important, such as for public transport schedules. Nonetheless, usage is inconsistent: in the UK, train timetables will typically use 24-hour time, but road signs indicating time restrictions (e.g. on bus lanes) typically use 12-hour time, e.g. "Monday–Friday 6.30–8.30pm". The BBC website uses the 24-hour clock for its TV and radio programme listings, while BBC promotions for upcoming programmes give their times according to the 12-hour clock. Punctuation and spacing styles differ, even within English-speaking countries (6:30 p.m., 6:30 pm, 6.30pm, etc.).

...
Wikipedia