You can show time by using either the 24-hour or 12-hour clock.
- The 24-hour clock is the preferred format for international audiences and the format used in most computer systems, so use the 24-hour clock when possible.
- If the technology or interface that you're documenting shows or uses the 12-hour clock, then be consistent with the interface and use the 12-hour clock.
When you use the 24-hour clock to show time, use the following guidelines:
- Use a colon to separate the hours, minutes, and seconds.
- Show the hours, minutes, and seconds with two digits each, even if the leading digit is 0.
- If you need to show a time zone, use Coordinated Universal Time (UTC), and indicate the time-zone offset from UTC.
|18:00:00 to 20:30:00|
|10:30:00 (UTC -6) (refers to CT)|
When you use the 12-hour clock to show time, use the following guidelines:
- Use a colon to separate the hours and minutes. If the minutes are 00, you don't need to show them unless you're showing a span of time that includes a time with minutes.
- Use lowercase letters for abbreviations of ante meridiem (a.m.) and post meridiem (p.m.). Separate these abbreviations from the time with a space. Use periods in the abbreviations.
- When specifying time zones, show both the spelled-out name and the abbreviation. Show the name in lowercase letters; use uppercase letters and no periods for the abbreviation.
- Avoid references to standard and daylight saving time because the appropriate designation changes frequently. However, if you need to include such a reference, insert S (for standard) or D (for daylight) as the second character in the abbreviation.
- When referring to 12 a.m., use 12 midnight or just midnight. When referring to 12 p.m., use 12 noon or just noon.
|6:00 p.m. to 8:30 p.m.|
|10:30 a.m. central time (CT)|
|1:30 p.m. central standard time (CST)|