Although every representation of time displays hours, minutes, and seconds, the presentation order and separators vary greatly. In fact, there are sometimes many differences between regions within the same country. The time formatting might differ from one culture to another in one of the following ways:
- The use of either a 12-hour or 24-hour clock. Most European and Asian locales use the 24-hour clock instead of the 12-hour A.M./P.M. model used in the United States. Also, A.M./P.M. can be rendered in the language of the country, and in some languages comes before the time and not after it.
- The character used to separate hours, minutes, and seconds. Although the colon (:) is the character most used in separating the hours, minutes, and seconds, some Asian languages use ideographic characters. In addition, some locales require "h," ";m," and "s" as part of the display.
In the twelve-hour system, the abbreviations AM and PM mean, respectively, ante meridiem (before noon), and post meridiem (after noon). Thus 12:01 PM is 1 minute after noon, and 12:01 AM is 1 minute after midnight. In English-language IBM manuals, AM and PM are not used in connection with midnight and noon; instead, noon (or 12 noon), and midnight (or 12 midnight) are used. The meaning of 12:00 is undefined and remains ambiguous.
In the ISO/IEC twenty-four-hour system, 24:00 is midnight at the end of a day, and 00:01 is one minute after midnight of the next day. The sequence is 23:59, 24:00, 00:01. In ISO/IEC standard 8601, both 24:00 and 00:00 are allowed to indicate midnight, with 24:00 indicating the end of the day and 00:00 indicating the start of the next day.
Time zone information (such as EST, CST, GMT) is sometimes appended to the time data; the abbreviations are not uniform across countries. If data timestamps do not specify the geographical location and local time or a time zone, the Coordinated Universal Time (UTC, a precise form of Greenwich Mean Time or GMT) will be assumed.
Fractions of seconds
According to ISO/IEC standards ISO/IEC 3307 and ISO/IEC 1000, the decimal digits representing fractions of a second and seconds should be separated by the same character that represents the decimal separator (comma or period) for the country. (For example, Australia would use 9:02:00.000 and France would use 9:02:00,000. For other countries, see the section on numbers. The fractions could be tenths of a second (one digit), hundredths of a second (two digits), or thousandths of a second (three digits).
Examples
The examples represent the time of 14 hours, 45 minutes, 16 seconds. When further precision is required, fractions of seconds may be concatenated after a decimal separator appropriate to the country, as in 14:45:16.0300015. Some governments may require specific formats.
- The time format used in official Brazilian documents is 14h45min16s.
- Canadian French usage is 14 h 45 min 16 s. When less precision is needed, the seconds and minutes can be dropped:14 h 45 or 14 h. In Canadian English usage, it is much more common in newspapers to see 2:45:16 PM or 2:45 PM than the 24-hour usage, but the 24-hour clock is common in transportation and data processing.
- Switzerland may use several different time formats. Time of day may be indicated with minutes superscripted, as in
 Timestamps may be indicated as 14.45 h, while elapsed time may be noted as 14:45.
- Belgian official documents sometimes use 14.45.16.
- In Iceland, date and time when displayed together are separated by kl.. For example: 30. sept. 2004, kl. 14:45. Alternate time formats are 14.45 or 14 45.
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