Many parts of the world are moving from standard time to daylight saving time (also called summer time) this week, so I thought it would be a good time to talk about the phrase “daylight saving time” and time in general. I still have to think of the mnemonic “spring forward, fall back” every time we do this to figure out what to do with my clocks. Since it’s spring, I’ll be moving my clocks ahead Saturday night before I go to bed. Technically, the time changes at 2:00 a.m. on Sunday, but it’s not like I’m going to wait up just to change my clocks.

Daylight saving time

Britain and Germany were the first countries to institute a time change during World War I. When the United States joined the war, lawmakers agreed that moving the clocks was a good way to save energy, and in the official 1918 law that established the time change in the U.S., they named it “daylight saving time.” It is still generally agreed to be “daylight saving time” today, and not “savings time” (1, 2, 3)— no S at the end.

Remember the spelling by thinking that the whole idea was that people were saving energy. The words are not capitalized, and there’s no hyphen.

The preferred spelling is ‘daylight saving time.’

A sad footnote is that supposedly we don’t save energy anymore by switching to daylight saving time because the energy we save by not having to turn on the lights as early is more than offset by how much more we run our air conditioners while we’re home in the warmer evenings.

Next, we’ll talk about time zones.

Time zones

Most countries have signed on to the idea of a standard world time system. For us the world is divided into 24 time zones, and each zone differs by an hour from the time zone next to it. Not everyone uses this system though. Some time zones don’t participate in daylight saving time, and a few places divide their region into half-hour zones.

Actually, it’s even more complicated than that. Arizona, for example, doesn’t participate in daylight saving time, but other states in the same time zone do. So during standard time, it is the same time in Arizona and Utah, but during daylight saving time, it is an hour earlier in Arizona because Arizonans don’t “spring forward” like other regions in the same time zone.

If you need to indicate that a time is in a certain time zone, the simplest way to do it is to put the time zone abbreviation after the time: for Eastern Standard Time, write “4:30 p.m. EST.”

However, as many readers have noted over the years, it’s common for people not to know whether we’re in daylight saving time or standard time and to write EST throughout the year and not just during standard time. If you’re one of those people, it’s better to simply use “ET” as an abbreviation for “Eastern time” instead of getting it wrong.

Generally, you capitalize all the words when you’re writing the full name of the time zone and capitalize just the first part when you’re using a shortened version. For example, you capitalize all the words in “Pacific Standard Time” and “Pacific Daylight Time,” but just the word “Pacific” if you refer to simply “Pacific time.”

GMT and UTC

Multiple international listeners have suggested using GMT (Greenwich mean time) as an alternative because it is the same for everyone. GMT uses a 24-hour clock that’s tied to the time at the Royal Observatory in Greenwich, England.

The Associated Press includes the local time and GMT in some international stories, and when they do, it’s written in parentheses after the local time, so if a story includes Eastern Daylight Time and GMT, for example, it would be written as “5 p.m. EDT (2100 GMT).”

GMT is also known as Universal Coordinated Time, abbreviated UTC, and the time in other time zones outside of the Greenwich zone is sometimes written as a plus or minus offset from GMT, so the time in New York can also be referred to as GMT-5 or UTC-5.*

I noticed too that the abbreviation “UTC” doesn’t match the words “Universal Coordinated Time.” It turns out the abbreviation is a compromise meant to be acceptable to people speaking different languages. English doesn’t always win.

Zulu Time

And just to make things even more complicated, GMT or UTC are also sometimes known as “Zulu time.” According to TimeAndDate.com, the “Zulu time” designation is mostly used in aviation and in the military. The name comes from the fact that each time zone in GMT has an alphabetical letter designation, and the zone at the Royal Observatory is labeled Z. So the name “Zulu time” comes from the name for the letter Z in the NATO phonetic alphabet: Zulu. You know how A, B, and C, are “alpha,” “bravo,” “charlie”? Well, Z is “zulu.” The time zones in the U.S. are designated R, S, T, U, V, and W, from the Eastern time zone to the Hawaiian time zone.

Zulu time also uses the 24-hour clock and is written with a Z after the number with no space, and may be written with or without a colon in the number, according to TimeAndDate.com. You say it as “zero eight hundred Zulu,” for example, for eight o’clock in the morning.

Should we use a universal time designation?

Although GMT, UTC, and Zulu time are the same everywhere, and they might be an improvement over all our different time zones, they’re not the current standard in the general public in the United States. It may be good to use GMT if you regularly schedule meetings internationally, but I can’t recommend it yet for people who mainly communicate with other people in the U.S.

How to politely schedule a meeting

However, I do think it’s polite to describe your meeting times in the other person’s time zone. For example, I usually say something like, “Let’s talk at 9:00; that’s noon your time.” Just make sure you get the conversion right! I always use TimeAndDate.com to check on times in other cities. And still, a couple of times I year, I miss a meeting because someone doing the scheduling got the time zone conversion wrong. (And every time that happens, the “let’s use GMT” suggestion sounds a little better.)

AM and PM

There are at least two acceptable ways to write “a.m.” and “p.m.,” which are abbreviations for “ante meridiem” and “post meridiem.” “Ante meridiem” is Latin for “before noon” and “post meridiem” is Latin for “after noon.” Note that it is “meridieM” not “meridiaN.”

You can write “a.m.” and “p.m.” as lowercase letters with periods after them or as small capitals with or without periods (4, 5). Either way, there should be a space between the time and the “a.m.” or “p.m.” that follows. Although small capitals used to be the preferred style, it’s now more common to see lowercase letters followed by periods (“a.m.” and “p.m.”) (6). I suspect that’s because it’s a little bit of extra work to make small caps on a computer.

A listener named Rae asked whether it’s OK to write 2 p.m. without the zeroes instead of 2:00 p.m.? If you’re using Associated Press style, that’s how you’d write it, but Chicago style recommends including the zeroes. So it depends on what style guide you follow.

Noon and midnight

Remember how I said “a.m.” means “before noon” and “p.m.” means “after noon”? So what about noon, then? Technically, noon is neither a.m. nor p.m. Although it’s common to see noon written as 12:00 p.m. and midnight written as 12:00 a.m., it’s not correct and can confuse people. It’s better to stick with just the words “noon” and “midnight” (7, 8, 9).

In the morning

There are also a couple redundancies that relate to time.

For example, it’s redundant to say “8:00 a.m. in the morning.” By including the a.m. you’ve already indicated that it’s morning.

Period of time

It’s also usually redundant to use the phrase “period of time” — either “period” alone or “time” alone will usually suffice (10, 11, 12). Merriam-Webster’s Dictionary of English Usage argues that occasionally using the full phrase “period of time” adds clarity (13), but I’m willing to bet that 19 times out of 20 you can use either “period” or “time” without causing confusion, but if you run into a sentence in which you really think you need it, go ahead.

I hope that helped, and if you live somewhere that observes daylight saving time, remember to move your clocks forward Saturday night before you go to bed.

References

1. Merriam-Webster’s Dictionary of English Usage. Springfield: Merriam-Webster, 1994, p. 828.
2. “daylight saving time.” AP Stylebook, 2019 edition. Click to check for reference (accessed March 1, 2020)
3. “time.” New York Times Manual of Style and Usage, 5th edition. p. 318.
4. “Numerals versus words for time of day,” The Chicago Manual of Style. 17th edition. Chicago: The University of Chicago Press, 2017, section 9.37. Click to check for reference (accessed February 29, 2020)
5. “Date and Time,” The American Heritage Guide to Contemporary Usage and Style. Boston: Houghton Mifflin Company, 2005, p.131.
6. Garner, B. Garner’s Modern English Usage. Second edition. Oxford: Oxford University Press, 2003, p. 39.
7. “noon and midnight.” The Chicago Manual of Style. 17th edition. Chicago: University of Chicago Press, 2017, p. 10. 9.38. Click to check for reference (accessed February 29, 2020)
8. Garner, B. Garner’s Modern American Usage. Second edition. Oxford: Oxford University Press, 2003, p. 39.
9. Goldstein, N., ed. The Associated Press Stylebook and Libel Manual. Reading: Perseus Books, 1998, p. 208.
10. Garner, B. Garner’s Modern American Usage. Third edition. Oxford: Oxford University Press, 2009, p. 619.
11. Garner, B. Garner’s Modern American Usage. Second edition. Oxford: Oxford University Press, 2003, p. 599.
12. Brians, P. Common Errors in English Usage. Wilsonville: William, James & Co., 2003, p. 205.
13. Merriam-Webster’s Dictionary of English Usage. Springfield: Merriam-Webster, 1994, p. 728.

* A reader asked me to clarify that “GMT is a time zone based on astronomical observations whereas UTC is an atomic time standard that is adjusted to keep step with GMT.”