A Primer on Writing about Time

Rachel Diebel Grammar, Writing Tips

Time is such an integral part of our experience as humans that we have a dozen different phrases and sayings about it—we run out of time, time is money, time heals, time flies. But when it comes to writing about time, there are often inconsistencies or variations in how we indicate years and time zones or whether it’s noon or midnight.

Following are some widely accepted guidelines to help you write about time as accurately and clearly as possible.

Years, Months, and Time of Day

Years, months, and time of day are the most common ways to distinguish time. Some pointers for referencing them follow:


Always use the numeral form for writing years unless it starts the sentence. It may be worth rewriting your sentence to avoid the long opening.

  • Nineteen seventy was a sad year for rock and roll, with the dramatic breakup of the Beatles.
  • In 1970, the dramatic breakup of the Beatles shook the world of rock and roll.

In informal writing, you can replace the first two digits of the year with an apostrophe.

  • The Beatles reigned over rock and roll in the ‘60s.


For specific dates, use cardinal numbers (1, 2, 3) rather than ordinals (1st, 2nd, 3rd). When a day is mentioned without a month or year, spell it out.

  • My daughter was born on April 15, 2013.
  • Decorations started to go up on December 1. By the twenty-fifth, they were everywhere.


When writing about the time of day, follow a few basic rules. First, spell out the number when you are talking about even, half, or quarter hours, as well as when using o’clock.

  • It’s half past four. We need to leave at a quarter to five.
  • My workday ends at six o’clock.

Use of noon and midnight is usually preferred to 12:00 p.m. and 12:00 a.m. to avoid confusion.

  • We will need to be out of the building before midnight.
  • The contest starts at noon on Thursday.

If you are emphasizing exact times, use numerals.

  • The plane leaves at 7:43 a.m. tomorrow.

When indicating whether the time is a.m. (ante meridiem) or p.m. (post meridiem), Chicago Manual of Style (CMOS) recommends using lowercase letters with periods, but it is also acceptable to use small caps, with or without periods. Whichever option you choose, be consistent within one body of text.

  • The conference will end at 4:00 p.m. (Correct, recommended)
  • The conference will end at 4:00 PM. (Correct)

Finally, avoid redundancy. You never need to use a.m. and in the morning together, nor p.m. and in the afternoon or in the evening.

  • The alarm is scheduled for 6:00 a.m. (Correct)
  • The alarm is scheduled for six in the morning. (Correct)
  • The alarm is scheduled for 6:00 a.m. in the morning. (Incorrect)

Time Zones and Daylight Saving Time

Daylight saving time is alternately dreaded and anticipated in the parts of the world that use it. It can mean an extra hour of sleep or a groggy morning after losing an hour.

Although in informal speaking we often add an s (daylight savings) when discussing daylight saving time, the official phrase does not contain the s and is never capitalized. A hyphen (daylight-saving time) is optional and a matter of house style choices.

Although in informal speaking we often add an s (daylight savings) when discussing daylight saving time, the official phrase does not contain the s and is never capitalized. #grammartip Click To Tweet

If your audience spans different time zones, you’ll want to indicate which time zone you are referring to in your writing. This can be done by adding the time zone abbreviation (see CMOS section 10.41, 17th edition, which recommends placing the time zone in parentheses after the time).

  • Join us for our next Twitter chat this Friday at 3 p.m. (PST).

Remember that a location observing daylight saving time is not in “standard time.” The correct way to write this would be PDT, for Pacific daylight time, rather than PST for Pacific standard time. For a list of worldwide time zone abbreviations for both standard and daylight saving times, visit here.

International Communication

The International Organization for Standardization (ISO) has specific recommendations to make international communication easier. If your audience is international, you should know the ISO’s recommendations for writing about time.

ISO Time Format

ISO 8601, the ISO’s standards for date and time format, recommends the twenty-four-hour time system, which is used by the military, scientists, and most countries outside of the United States.

Twenty-four-hour time is expressed in four digits (unless you are including seconds in the time) and can be written with or without the colon, although the ISO does recommend using a colon for clarity. What we would typically write as 7:35 p.m. would be written as 19:35 under ISO 8601.

ISO Date Format

Additionally, the ISO recommends using a year-month-day format for indicating the date, which counteracts the confusion between the US month-day-year format and the day-month-year format used in much of the rest of the world.

Log in to the new user portal starting on 06/05/19. (Unclear, as it could be interpreted as June 5, 2019 or May 6, 2019, depending on which country the user lives in)

Log in to the new user portal starting on 2019-06-05. (Clear)

Closing Time

If your job requires writing about time—whether you’re simply scheduling meetings over email or carefully preparing a document for publication—knowing these rules will help ensure your audience understands your meaning, even if they’re working on one less hour of sleep after daylight saving!


Does remembering style guidelines feel as impossible to you as time travel? Work with one of the Scribe Source’s proofreaders to catch the details you may have missed.

About the Author

In addition to being a great editor, Rachel has a kind soul and an infectious smile that makes you want to take off for a playday with her. It makes sense that her primary area of specialty is children’s literature in addition to K–12 curriculum. She joined the Scribe Source in 2016.