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Why I Switched to Twenty-Four Hour Time

Updated: Jul 25, 2021

When I was attending the University of Oregon, I worked as an English-Language Conversation Partner with ESL (English as a Second Language) students at the American English Institute. My primary role was to have conversations in English about topics they would not be familiar with (such as Thanksgiving, the three branches of American government, and the Second Amendment). Since I was usually the one introducing these students to novel and unfamiliar ideas, imagine my surprise when a young Japanese man introduced me to a completely new method of time-keeping!

A Quick Summary of Twelve Hour Timekeeping

If you live in the United States or a nation that used to be part of the British Empire, it is likely that the dominant system of timekeeping divides each 24-hour day into two periods of twelve hours. Since 24/12=2, each hour occurs twice in a day. Therefore, nations that use twelve-hour clocks must also append something akin to "AM" or "PM" after each hour to clarify whether the hour is before or after Noon. In twelve-hour timekeeping, however, it is nearly impossible to determine whether midnight is 12am or 12pm, since it could be both or neither, depending on the definition. If the wide variety of conflicting responses to this query are anything to go by, the twelve-hour system of timekeeping is anything but precise.

Here is a list of the hours in twelve hour timekeeping:

  • Midnight (12:00am of a new day or 12:00pm of the previous night)

  • 01:00am

  • 02:00am

  • 03:00am

  • 04:00am

  • 05:00am

  • 06:00am

  • 07:00am

  • 08:00am

  • 09:00am

  • 10:00am

  • 11:00am

  • Noon (12:00m or 12:00pm of a day that starts with 12:00am, or 12:00am of a day that starts with 12:00pm)

  • 01:00pm

  • 02:00pm

  • 03:00pm

  • 04:00pm

  • 05:00pm

  • 06:00pm

  • 07:00pm

  • 08:00pm

  • 09:00pm

  • 10:00pm

  • 11:00pm

  • Midnight (12:00am of a new day or 12:00pm of the previous night)

A Quick Introduction to Twenty-Four Hour Timekeeping

My conversation partner explained that Japan uses twenty-four hour time, instead of the twelve-hour time most Americans are familiar with. Unlike twelve hour time, each 24-hour day is divided into exactly 24 hours, each with a different name. Because each hour's name is only used once per day, there is no need to append "AM" or "PM" after each hour. Instead of times stopping at 12:00 and restarting back at 00:01 at both noon and midnight, twenty-four hour time starts at 00:00 (midnight) and runs all the way up to 23:59 (just before midnight) before restarting the next day. Under this system, midnight is clearly always the start of a new day at 00:00, and noon is clearly always 12:00 in the middle of each day.

Here is a list of the hours in twenty-four hour timekeeping:

  • 00:00 (Midnight, start of the day)

  • 01:00

  • 02:00

  • 03:00

  • 04:00

  • 05:00

  • 06:00

  • 07:00

  • 08:00

  • 09:00

  • 10:00

  • 11:00

  • 12:00 (Noon, middle of the day)

  • 13:00

  • 14:00

  • 15:00

  • 16:00

  • 17:00

  • 18:00

  • 19:00

  • 20:00

  • 21:00

  • 22:00

  • 23:00

  • 24:00 (Midnight, end of the day)

Do you see the pattern? It's a lot simpler than twelve-hour time, don't you think? Basically, the numbers start at zero at the beginning of the day and incrementally increase throughout the day until the day ends and a new day begins.

A Brief Explanation for the Existence of Twelve Hour and Twenty-Four Hour Timekeeping

Although twelve hour timekeeping was originally brought to America by the British, most individuals did not possess timepieces during the colonial era. Life was a bit simpler then, so they tended to keep time based upon the sun's position in the sky. Schoolchildren were called to school by the tolling of school bells, and churchgoers were called to church by the tolling of church bells. However, with the arrival of trains that connected far-flung reaches of the continent, journeys that once took weeks now only took a matter of days or hours. Formerly remote town and villages were now interconnected with one another, and suddenly the differences in timekeeping became a serious problem for scheduling train arrivals and departures. Partly for this reason, timezones were standardized and twelve hour clocks were synced up and spread across America. This served the fledgling country well for a century, but we are no longer in the age of steam locomotives and horse-drawn carriages.

With the conclusion of World War II, Japan made a quantum leap into the future with a brand-new transportation system. Unlike the American Amtrak rail system that is often hours behind schedule, the Japanese pride themselves on maintaining a wide-reaching network of bullet trains on split-second precision schedules. However, this is only possible with Japan's usage of twenty-four hour time. In order to make it easier to calculate travel times in Japan, twenty-four hour time was introduced to permit commuters to simply subtract their departure time from their arrival time. Since the arrival time is always later than the departure time, the math is simple. For example, a Japanese businessman who catches a train that leaves at 09:00 and will arrive at its destination at 14:00 intuitively understands that the total length of the trip will be 5 hours. The math for American timetables is not so straightforward.

A Major Advantage of Twenty-Four Hour Timekeeping

At this point, you are no doubt wondering if the use of twenty-four hour time is limited to Japanese train schedules. Thankfully, it is not. For example, most militaries use twenty-four hour time to avoid confusion when scheduling coordinated attacks and troop movements. On a more local level, many late-night bars in Japan also use twenty-four hour time in a very clever way.

Consider for a moment that most bars open in the late afternoon or late evening and stay open until the early morning. However, if the sign for a restaurant says "Open 5 to 2," the sign could be ambiguously interpreted as saying that the restaurant is open from 5 in the morning to 2 in the afternoon, or from 5 in the evening to 2 in the morning. With the standard implementation of twenty-four hour time, the sign would read "Open 17 to 2," which is certainly less ambiguous (it can only mean that the bar opens five hours after noon and stays open until two hours past midnight), but still results in a less-than-satisfactory appearance, since the closing time has a smaller number than the opening time. In Japan, it is common practice for establishments that stay open past midnight (and thus bridge the gap from one day to the next) to keep counting hours past 24:00. With this in mind, our hypothetical restaurant would post a sign stating "Open 17 to 26," and it would be clear that the restaurant is both open two hours past midnight and it is open for a total of 9 hours.

Here's a practical example from my own life: When I worked at the Disneyland Resort in Anaheim, California, my shifts were posted weekly. The hours of my shifts were written in twenty-four hour time. This is because the resort operated 24/7/365. Many cast members (including myself) worked the late-night or graveyard shift, which meant that they started in the late evening and ended in the early morning. If twenty-four hour time wasn't used, these shifts would look identical on paper to shifts that started in the late morning and ended in the early afternoon. To avoid confusion, Disney adopted twenty-four hour time for its shift schedules. As a result, nearly all Cast Members adopted twenty-four hour time in their personal lives, as well (including me). Once I got started, however, the advantages were so apparent that I couldn't stop. Even though I now work a more traditional eight-hour shift at the University of Oregon, I still use twenty-four time.

A Side-By-Side Comparison of the Two Systems of Timekeeping

Now that I have explained the differences between twelve hour and twenty-four hour timekeeping, you might find it helpful to see a side-by-side comparison chart that maps one system onto the other for easy conversion. Thankfully, this process is much more straightforward than that of converting degrees Fahrenheit to degrees Celcius.

Here are the two time keeping systems side-by-side for easy comparison (Twenty-four hour time is on the left, and twelve-hour time is on the right):

  • 00:00 =12:00am or 12:00pm (Midnight)

  • 01:00 = 01:00am

  • 02:00 = 02:00am

  • 03:00 = 03:00am

  • 04:00 = 04:00am

  • 05:00 = 05:00am

  • 06:00 = 06:00am

  • 07:00 = 07:00am

  • 08:00 = 08:00am

  • 09:00 = 09:00am

  • 10:00 = 10:00am

  • 11:00 = 11:00am

  • 12:00 = 12:00am or 12:00pm or 12:00m (Noon)

  • 13:00 = 1:00pm

  • 14:00 = 2:00pm

  • 15:00 = 3:00pm

  • 16:00 = 4:00pm

  • 17:00 = 5:00pm

  • 18:00 = 6:00pm

  • 19:00 = 7:00pm

  • 20:00 = 8:00pm

  • 21:00 = 9:00pm

  • 22:00 = 10:00pm

  • 23:00 = 11:00pm

  • 24:00 = 12:00pm or 12:00am (Midnight)

From the side-by-side comparison above, you can clearly see that the twenty-four hour time system also has a great deal more visual balance, better symmetry, and less visual clutter than the twelve hour time system.

Now that I have clearly enumerated all of the advantages that twenty-four hour time has over twelve hour time, it seems absurd to me that we still use twelve-hour time. It's possible, after all, to start using twenty-four hour time without replacing twelve hour clocks. And yet we have to teach our kids a head-scratching, convoluted system that requires repeating the same time twice in one day! How did we get here? Actually, that's not important. What really matters is how we get out of it.

Well begun is half done." - Benjamin Franklin

If you think about it, we already acknowledge that each day has twenty-four hours. All we need to do is start acting like that is true. Please join me in the twenty-four hour revolution. It's as easy as switching a setting on your smartphone. Really, it's that simple.

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