How is time measured in our invented world? This is a subject we can ignore if everything is Earth-like and we’re fine with the audience assuming time is similar, as they probably will unless we remark on it. Markedly different time measurement is an area of unnecessary exposition that is best avoided unless it matters for our work. Readers don’t want to remember how many minutes there are in an hour, hours in a day, how long the week is, how many weeks there are per month, and how many months the year includes. Each time we mention that two characters will meet in an hour, but that’s really two Earth hours, is an annoyance.
Should we create different time measurements? That depends.
Minutes and Hours
I recommend leaving minutes and hour lengths alone. Changing them offers an audience confusion with no payoff. There are better ways to make our world seem different. Even if we mention that an hour is ninety minutes, for example, but then we keep writing “hour” in our story, the reader will forget the different length. This is especially true if this alteration is arbitrary and has no rationale that makes it easier to remember. We can invent other words instead of “hour,” but then those require explanations that must be remembered, too, doubling down on the encumbrance with which we’ve burdened the audience.
While it’s true that time is likely measured differently on other planets, our audience is on Earth and needs to quickly understand time references in Earth terms. A workaround in SF that has characters from Earth is to have one mention “that’s 1.5 Earth hours” to another person; the characters should likely go by Earth measurements for their comfort and that of the audience. In SF, a briefly visited planet is a good time to use different minute/hour measurements for a story impacted by this.
One reason to leave minutes and hours alone is that this unit of time measurement will be more frequently mentioned than days, weeks, or months. Story scenes take place in minutes, hours, and days. Having “minute” and “hour” be too different just messes with our audience’s understanding of time. But scenes are less often separated by weeks or months, and once we’re working in bigger units, does it really matter if “three months later” is one hundred days instead of ninety? Only a little.
As an example, on my world of Llurien, there are twelve months of twenty-eight days, resulting in 336 days. That’s twenty-nine days, or a month, shorter than Earth. This means someone a year old on Llurien is eleven months old on Earth. But after ten years, a ten-year-old on Llurien would only be nine years old on Earth. While the gap has widened, the difference between a nine and ten year old isn’t great. This is again true at 22 vs 20, and 33 vs 30. I don’t need to ever point this out to my audience, but if I do, it doesn’t matter unless characters from Llurien come to Earth (or vice versa).
On this note, it’s important to figure out how long a year really is on an invented world. Once we’ve decided on all our measurements, do the math to figure out a scenario like the above.
We could name the hours of the day, but this can be another encumbrance that gains us little and requires exposition. Do so with a good reason that impacts your story or skip it. We can do these things and seldom mention them, however.
We can change the number of hours in a day, but it’s recommended that day lengths be similar to Earth if we’re building an Earth-like world. This means being off by a few hours at most, not having only twelve hour days unless we really mean for this to figure prominently. In SF, the life forms from a planet with different length days will have different sleep and eating cycles, but this will matter more when life forms from worlds with disparate cycles are brought together.
Days in a Week
The number of days in a week is another area we can change. There are seven days on Earth due to ancient civilizations naming them after seven celestial bodies that were visible (this included the sun and moon, which are Sunday and Monday respectively). With planets named after gods like Thor (Thursday), we also acquired the names. We can do something similar on an invented world, using whatever rationalization we can make sensible. There could be eight moons that cause eight-day weeks. There could be six gods, each getting a day in a six-day week. We can depart from deities and decide the days are named after the six schools of magic in a world dominated by supernatural power. Or maybe there were six great heroes from long ago. Or six dragons. In SF, the days of the week are likely decided long before technological advances that could have days named after technology (or related scientists, explorers, etc.), but maybe a later empire forced change on everyone.
In the above examples from Earth, you’ll note that Thor is spelled differently for Thursday. Most of the god names were altered in time from different cultures misspelling things, or just altering the spelling for their native language. We might want to do this, too, to make day names easier to say. For example, I could call a day Llurienday, but that’s kind of a mouthful. Shortening it to Llurday or Rienday is a little better.
Regardless of our decision, we should take strides to minimize the use of day names in our writing because our audience will have no idea what we’re talking about. This is true even if we explain it once. We can provide charts on a website, like a glossary, but skillfully handling this is the best approach. Our characters (as opposed to our narration) should be the ones most often using the day names, because they would. Take this example passage:
Kier asked, “When will the sword be ready?”
“Next Rienday,” the blacksmith replied.
Kier nodded. A week and a day. Plenty of time to run it through his beloved’s heart. (italics)
If we change the number of days in a week, we might want to go with six or eight. The reason is that when we narrate “a week and a day” as above, this is still close to a week on Earth and the audience’s sense of time passing is only slightly off. By contrast, if a week is twelve days, we throw the audience off quite a bit more and might have to keep reminding them of such a thing. In the above scenario, I would instead write, “Thirteen days. Plenty of time…”
Weeks in a Month
How many weeks do we want in a month? On Earth, this isn’t set. Instead the number of days in a month is what determines how weeks are laid out. A month with thirty days could span four weeks one year and five the next, depending on what day of the week that month began. We might choose to standardize the weeks more, in which case the weeks might get names. On my Llurien world, every month has four weeks of seven days. Those weeks are associated with the four elements, resulting in Fireweek, for example. The fourteenth day is always the seventh day of the second week. No one needs a calendar to figure it out.
Months in a Year
How many months do we want in a year? Once again, and for the same reason, it’s recommended to be off by one from Earth, meaning eleven or thirteen months in a year. Earth months are named and our invented world will need month names, too. Once again, our audience will have no idea what we’re talking about, so they should be used sparingly and explained succinctly. Take this example passage:
Kier asked, “When will the dragon give birth?”
“In Dicerimon,” the dragon keeper replied.
Kier nodded. Three months, just in time for the winter sacrifice.
In this passage, note the use of the suffix “mon” on the month name. On Earth, we have “uary” and “ber” to denote half of the months. We might want to choose a similar approach to indicate to our audience that we’re referencing a month. A common prefix or suffix can assist their understanding. As with Earth, perfect uniformity may not happen or be advisable and can even look like too much planning on our part. Feel free to make exceptions.
When revealing the number of months, we can also work this into narration instead of writing exposition about it. See Kier’s fate for guidance:
Kier asked, “When will I be executed for my crimes?”
“Two years from today,” the judge replied. “One for your beloved. Another for the dragon.”
Kier hung limp in the chains. Twenty-two months to agonize over his mistakes.