In the Zone: It’s About Time - The Blue Book of Grammar and Punctuation (2023)

We’re all aware of how vital marked and measured time is to guiding and structuring our days. How then do we treat it in precise and careful writing?

We offered some guidelines in our updated April 2017 articleWriting Dates and Times. We’ll expand on those here by delving deeper into the most recent editions of two of our primary style references,The Chicago Manual of Style,which commonly applies to formal publications (e.g., fiction and nonfiction books, textbooks, academic reports) andThe Associated Press Stylebook,which often helps in advising journalistic and daily writing (e.g., newspapers, magazines, business marketing, and correspondence).

According toCMOS,if we’re referring to times of day in even, half, and quarter hours, we would usually spell them out in writing. The number is always spelled out witho’clock.

Examples:
With the rain delay, the game probably won’t be over until at least ten o’clock.
The men’s open-gym basketball games usually end around a quarter of nine.

When referencing exact times, we would use numerals, including zeros for even hours.

Examples:
The class is scheduled to begin at 7:00 this morning.
Our flight leaves at 8:25 tomorrow evening.

For abbreviated day divisions,CMOSrecommends a.m. forante meridiem(before noon) and p.m. forpost meridiem(after noon). These abbreviations also may be set in small caps with numerals.

Examples:
9:23 p.m.
7:47 a.m.
6:00A.M.

It further points out that a.m. and p.m. should not be used withmorning, noon, afternoon, evening,night, ormidnight, nor should they be used witho’clock.

Incorrect:5:45 p.m. in the afternoon
Correct:5:45 p.m.,5:45P.M., or5:45 in the afternoon

Incorrect:six o’clock a.m. this morning
Correct:six o’clock this morning

Formidnightandnoon, CMOSadvises not to use numbers except informally in an expression such astwelve o’clock at night.Becausenoonis technically 12:00 m. (meridies,or mid-day), writing or saying12:00 p.m.(after noon) would be unclear as well as illogical. For certain references tomidnight,a double date might be included for clarity:Richard was born at midnight, November 13–14.

APuses only figures for times and does not include them withnoonandmidnight.It also omits zeros for even hours andsets day divisions in lowercase letters.

Examples:
Breakfast is at 9 a.m.
Lunch is at noon.
The next meeting is at 3:30 p.m.
The observatory program begins tonight at midnight.

LikeCMOS, APdirects to avoid such redundancies as10 a.m. this morningand10 p.m. tonight.It also citeso’clockconstructions as acceptable but prefers that time be written with numerals and a.m. or p.m.

Time Zones

In scientific theory, Earth has 24 time zones, each a one-hour zone 15 degrees wide to indicate a one-hour difference in mean solar time. Politically, however, time zones are further influenced by how internal and international borders are drawn. Some of these zones have only 30- and 45-minute offsets, increasing the world’s total number of zones. The International Date Line also creates three more zones.

(For more information about the world’s time zones, as well as the difference between standard time and daylight saving time, clickhere. BothCMOSandAPagree that the proper term isdaylight saving[notsavings]time.)

According toCMOS,time-zone descriptions are spelled out and lowercased except for proper nouns. Abbreviations are capitalized:

Examples (using time zones commonly referred to in the U.S.):
Pacific standard time (PST)
mountain standard time (MST)
central daylight time (CDT)
eastern daylight time (EDT)

Reference to a specific time and zone would follow standard guidelines with the zone in parentheses: 4:42 p.m. (PST), 11:03 a.m. (MDT), 2:30 p.m. (CST), 10:00 P.M. (EST).

APon the other hand advises to capitalize the full name of each time zone: Pacific/Mountain/Central/Eastern Standard Time. It also abbreviates them with all caps asCMOSdoes.

It does not set off the abbreviations with commas or parentheses. In addition, it cites them as acceptable on first reference for times used within the continental U.S., Canada, and Mexico only if the abbreviation appears with a specific time (e.g., midnight CST, 11 a.m. MST).

For time references without a specific clock reading,APdirects to spell outtime zone(lowercase) and treat the region as proper.

Examples:
Mountain time zone
Milwaukee is in the Central time zone.
In California they go by Pacific time.

How you write time will typically be determined by your format (formal or journalistic/daily). It may also be influenced by your personal preference; the key as always is to choose your style and remain consistent. Combined with our April 2017article, these guidelines can help you be right on time.

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If the article or the existing discussions do not address a thought or question you have on the subject, please use the "Comment" box at the bottom of this page.

32 responses to “In the Zone: It’s About Time”

  1. Bill Wei says:

    August 8, 2018, at 8:11 am

    Maybe I’m old, but I don’t recall ever having learned the phrase “quarter OF nine” in grade school. In fact, until I read this blog, I never heard of the phrase. For me, it is either “quarter TO nine” or “quarter PAST nine”. The only thing I can think of which might be similar is the use in British English of the phrase “half nine”, which for people like me who also speak other European languages is very confusing, since “half nine” means 9:30 in British English and 8:30 in any other European language.

    • GrammarBook.com says:

      August 13, 2018, at 11:50 am

      The Chicago Manual of Style contains this section:

      “Times of day in even, half, and quarter hours are usually spelled out in text. With o’clock, the number is always spelled out. In the third example, the a before quarter is optional.

      Her day begins at five o’clock in the morning.
      The meeting continued until half past three.
      He left the office at a quarter of four (or a quarter to four).
      We will resume at ten thirty.
      Cinderella almost forgot that she should leave the ball before midnight.”

  2. Steve Rosenberg says:

    August 8, 2018, at 8:32 am

    Any thoughts on military time? Much of the above discussion would be unnecessary if we got used to using it.

  3. Shannon Brown says:

    August 8, 2018, at 9:23 am

    Just a question. I am confused about “a quarter of nine” vs “a quarter to nine” vs “a quarter ’til nine.” Are all three correct or should we always use “a quarter of” to denote before the hour?

    • GrammarBook.com says:

      August 13, 2018, at 11:52 am

      The Chicago Manual of Style contains this section:

      “Times of day in even, half, and quarter hours are usually spelled out in text. With o’clock, the number is always spelled out. In the third example, the a before quarter is optional.

      Her day begins at five o’clock in the morning.
      The meeting continued until half past three.
      He left the office at a quarter of four (or a quarter to four).
      We will resume at ten thirty.
      Cinderella almost forgot that she should leave the ball before midnight.”

  4. Kamal Taylor says:

    August 8, 2018, at 2:07 pm

    Until I read your article, I was unaware of the correct spelling of AM as ante meridiem. I had to check Merriam-Webster, and the word I thought I was using, antemeridian, refers to before noon or occurring in the forenoon, https://www.merriam-webster.com/dictionary/antemeridian. As they are both before 12:00 pm, I am not sure why the division was ever necessary, but that’s language.

    Interestingly enough, there seems to be confusion between the References out there. While both Merriam-Webster and OED both indicate it means before noon or midday, the American Heritage Dictionary specifies it as exactly 10:30, https://www.ahdictionary.com/word/search.html?q=ante+meridiem.

    Great article.

    • GrammarBook.com says:

      August 13, 2018, at 12:43 pm

      As we understand it, ante meridiem is the term that’s abbreviated as a.m. and used with numerals to designate specific times, while antemeridian is an adjective referring to something occurring before noon, such as an antemeridian activity. Such use is rare these days.

      The American Heritage online entry using 10:30 AM is simply intended as an example of the abbreviated form of ante meridiem. It isn’t meant to imply that the term ante meridiem means 10:30.
      “Before noon. Used chiefly in the abbreviated form to specify the hour: 10:30 A.M.; an A.M. appointment.

  5. Shiv A. says:

    August 25, 2018, at 3:09 pm

    I would write “Quarter past nine.”

    • GrammarBook.com says:

      August 25, 2018, at 3:10 pm

      A “quarter past nine” is fine. A “quarter of nine” is another way of saying a “quarter to nine.”

  6. Jakob says:

    November 14, 2018, at 4:37 am

    I would like to send a correct save-the-date card in English for my wedding. It happens on July 5th and 6th, 2019. How do you write it correctly on the card: “July 5th and 6th, 2019,” or “July 5-6, 2019,” or “July 5/6, 2019”?

    • GrammarBook.com says:

      November 17, 2018, at 10:42 pm

      Invitations have their own sets of rules and styles and are not always the same as formal writing. That being said, we would rule out “July 5/6.”

  7. Lauren D says:

    January 7, 2020, at 4:40 pm

    Is there a rule that ignores DST? My organization uses AP Style and I am writing about recurring meeting time throughout the year that will be based on the central time zone. Would it be acceptable to simply write “Teams will meet on the first Friday of the month at 2:30 p.m. central”?

    • GrammarBook.com says:

      January 8, 2020, at 8:24 pm

      AP advises capitalizing the region, so you could write “Teams will meet on the first Friday of the month at 2:30 p.m. Central time.”

  8. Emily Lower says:

    March 21, 2020, at 6:48 pm

    Has anyone noticed the irony that this website posts the time of our entries in what seems like an incorrect way – as I understand via grammarbook.com and other sites? For example, the post before was made on January 8, 2020, at 8:24 pm. (pm – not p.m. or PM or P.M.)

    I teach college part-time and always correct students if they write as above.

    In the big scheme of things this may not be that important, but I know I look to support students’ writing in a clearer and more professional manner.

    • GrammarBook.com says:

      March 27, 2020, at 12:00 pm

      You’re correct that it’s not that important. In this article we mention the abbreviation preferences of The Chicago Manual of Style and the Associated Press Stylebook. However, there are many variations you can find in newspapers, magazines, and books both in print and online. The Chicago Manual of Style acknowledges in Rule 10.41 that “…these sometimes appear in small capitals (with or without periods) ….” In our April 19, 2017, post Writing Dates and Times, cited in our above article, you will find the following:

      Note: You may use AM and PM, A.M. and P.M., am and pm, or a.m. and p.m.
      Some put a space after the numeral, others do not.

      Example: Her flight leaves at 6:22 a.m.
      Example: Her flight leaves at 6:22am.
      Example: Please arrive by 12:30 P.M. sharp.

      We also mention these approaches in our Rules for Writing Numbers.

      Given all that, our own preference would have been to write the example you gave as “8:24 p.m.” However, the style without periods is used by the commercial software that manages our comments and responses, and it’s perfectly acceptable. When there are several options to choose from in this and other areas of English grammar and punctuation, our recommendation is to choose a method and be consistent.

  9. mbali says:

    July 29, 2020, at 9:57 am

    Is 5:00 p.m. Pacific Time written correctly?

    • GrammarBook.com says:

      August 3, 2020, at 1:13 pm

      That is acceptable as an informal response. More formally, according to AP style, you could write 5:00 p.m. Pacific Standard [or Daylight]Time.

  10. Erica says:

    January 15, 2021, at 10:44 am

    When using time zones can you use a 2 letter abbreviation instead of a 3 letter abbreviation? For example, ET for Eastern instead of EST Eastern Standard? This would eliminate the need to remember when day light savings ends and begins. I do notice that most sites are using the 3 letter abbreviation. I am just not sure which is considered proper.

    • GrammarBook.com says:

      January 21, 2021, at 2:02 pm

      Your approach assumes people will understand the subtle difference between ET and EST. If you choose not to observe daylight saving time and are communicating with individuals in various time zones, that adjustment should be clear in your communication to avoid potential confusion.

  11. Dee Lindholm says:

    March 24, 2021, at 2:55 pm

    What is the correct spelling?
    day-time
    daytime
    day time
    night-time
    nighttime
    night time

    Thanks so much!

  12. Karen Baker says:

    May 3, 2021, at 5:02 pm

    In print pieces that will remain current for several years, when showing the hours of operation for a calling center or business, should the time zone include the “S” or “D” in the middle or just a more generic “ET,” for example?

    • GrammarBook.com says:

      May 6, 2021, at 11:58 am

      Please see our January 21, 2021, reply to Erica.

  13. Rich says:

    June 14, 2021, at 7:11 am

    I am having a difficult time sorting exactly how international date line should be written?
    International Date Line
    International Dateline
    international date line
    international dateline?

    It’s for a non-fiction book. Thanks.

    • GrammarBook.com says:

      June 15, 2021, at 11:36 am

      AP Stylebook and Merriam-Webster both write it as “international date line.”

  14. Jane W. says:

    August 12, 2021, at 3:20 pm

    If you’re saying that a meeting will take place at 9:00 a.m. Eastern Time and 12 noon Pacific Time, isn’t it proper to list the Eastern Time first followed by the Pacific Time?
    Is it ever proper to list the Pacific Time first? The meeting will be attended by people on both coasts.

    • GrammarBook.com says:

      August 18, 2021, at 8:39 pm

      We are not familiar with specific, definitive guidelines concerning the sequence of identifying time zones. A common practice can be to begin with the time zone in which the event is taking place (e.g., a meeting in New York is identified as 9:00 a.m. EST and 6:00 a.m. PST [as Pacific time is three hours earlier than Eastern time]).

  15. Miguel Aguiar says:

    October 30, 2021, at 12:52 pm

    For example, Lisbon time is UTC and Brussels time is UTC+1. What’s the correct way for saying the difference between the two cities? Lisbon is “one hour earlier”, “one hour ahead”, or “one hour behind” than Brussels?

    • GrammarBook.com says:

      November 8, 2021, at 5:18 pm

      UTC + 1 is one hour ahead.

  16. Judy Williams says:

    May 9, 2022, at 1:00 pm

    Do you say: I am in PST, or do you say I am on PST?

    • GrammarBook.com says:

      May 11, 2022, at 8:29 pm

      We prefer using the preposition “in” when referring to a time zone. Formal writing might be different than casual conversation.

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