Date and time terms

This section covers usage for terms related to time and date.

Term	Usage
24/7	Don't use. Use all day, every day, always, or something similar.
AM, PM	Use AM and PM (preceded by a space). Use capital letters for AM and PM. Examples 10:45 AM 6:30 PM
Dates	Use the following format for dates: month day, year, as in July 31, 2016. Don't use day month year, as in 31 July 2016. In UI, it's OK to use numbers and slashes for dates if the code supports that format and automatically displays the appropriate date format for different locales. Don't use ordinal numbers (such as 1st, 12th, or 23rd) to indicate a date. Examples February 16, 2016 2/16/16 (in UI)
Days of the week: Sunday–Saturday	Capitalize the days of the week. Don't use abbreviations unless space is extremely limited. Don't include a period with the abbreviations. Three-letter abbreviations are preferred: Sun, Mon, Tue, Wed, Thu, Fri, and Sat In calendars and date picker UI controls, it's OK to use two-letter or one-letter abbreviations: Su, Mo, Tu, We, Th, Fr, and Sa S, M, T, W, T, F, and S For the three-letter and two-letter abbreviations, use sentence-style capitalization (Su), not all uppercase (SU).
midnight, noon	Use noon and midnight. Don't use 12:00 noon and 12:00 midnight. Midnight is the beginning of the new day, not the end of the old one.
Months: January–December	Capitalize the names of months and their abbreviations. Don't use abbreviations unless space is extremely limited. Use three-letter abbreviations when necessary: Jan, Feb, Mar, Apr, May, Jun, Jul, Aug, Sep, Oct, Nov, and Dec Don't include a period with the abbreviations.
Seasons: autumn, winter, spring, summer	Don't refer to seasons if you can avoid it. Talk about months or calendar quarters instead. If you must mention a specific season, identify the hemisphere, too. (Summer in the northern hemisphere is winter in the southern hemisphere.) Don't capitalize the seasons except to designate an issue of a publication, such as Spring 2017.
Time, ranges of time	Use numerals for times of day: 2:00, 4:15, 7:30. Always include AM and PM. Include the time zone if you're discussing an event that customers beyond the local time zone might see or attend. In text, use to in a range of times. Example 10:00 AM to 2:00 PM In a schedule or listing, use an en dash with no spaces around it. Example 10:00 AM–2:00 PM Exception In a date range that includes two times and two dates, add spaces around the en dash. Lead with whatever is most important to the customer within the context: time of day or date. Examples 2:15 AM–4:45 PM 4/1/16 (time range on a single day) 12/1/17 2:15 PM – 4/1/18 4:45 PM (time plus date range)
Time zones: Eastern Time, Central Time, Mountain Time, Pacific Time, Coordinated Universal Time (UTC), Greenwich Mean Time (GMT)	Capitalize time zones. Don't abbreviate unless space is severely limited. If you must abbreviate, use ET, CT, MT, and PT. Don't specify standard time or daylight saving time unless you're providing information about a specific event where that information matters. If you're referring to a time zone as a geographical area, call it a zone. Example in the Pacific Time zone Not all time zones have names, and some time-zone names are used in more than one geographical area. If you're talking about a particular place, clarify the country or reference Coordinated Universal Time (UTC). Don't include spaces around the plus sign (+) or hyphen (-). Examples Eastern Time (UTC-5) Eastern Time (UTC+10) Eastern Time (Australia) For time zones without names, refer to the offset from Coordinated Universal Time. Example UTC+7 Don't abbreviate Coordinated Universal Time in text unless space is severely limited. Use UTC, never CUT. (It's OK to use UTC in references to a specific time zone, such as UTC+7.) Don't use Universal Time Coordinate or Universal Time Coordinated. Don't use Greenwich Mean Time or GMT by itself unless you have no other choice. Use Coordinated Universal Time instead. On the first mention, it's OK to refer to Coordinated Universal Time (Greenwich Mean Time).

Abbreviating units of time

Unit	Abbreviation
day, days	d Spell out except in UI or when space is extremely tight.
hour, hours	h
microsecond	Don't abbreviate.
millisecond, milliseconds	ms
minute, minutes	min
month, months	mo Spell out except in UI or when space is extremely tight.
nanosecond	Don't abbreviate.
second, seconds	sec
week, weeks	wk Spell out except in UI or when space is extremely tight.
year, years	yr Spell out except in UI or when space is extremely tight.