One of my Kingdom Come novels has the working title About Damn Time because the theme is that a visitor to Earth from Kingdom Come has trouble adjusting to Earth’s shorter days.
This is not about that novel, but it is about the way time is measured on Kingdom Come.
I understand that many science fiction universes use Earth time as a standard simply because it is convenient. It would be too much work for the reader to figure out a different system, which distracts and detracts from the actual story. However there are two natural facts about every planet that are very simple for any human to understand and are very influential to a human’s biologic clock: the length of a day (the planet’s rotation) and the length of a year (how long it takes the planet to go around the sun.)
On Luna, Earth’s moon, the year matches Earth but the day is much, much longer. More than 27 Earth days. That’s two weeks of darkness and two weeks of night. Of course, it makes sense for Lunar citizens to adopt Earth time. In my Lunar Shorts, I have the society use Greenwich Mean Time.
A Martian Day is very close to an Earth day, only about a half hour longer. The year is twice as long as Earth’s.
For my completely fictional planet Kingdom Come, I decided that the day and the year around one and a quarter times that of Earth. I’m currently playing with number so that the actual ratio is something 1.278 for days and something different for years, with leap years coming every 3 years out of 7.
That’s the easy part. The part I’m currently debating in my own head is how to divide that year and that day. For a while, I planned on dividing the year into ten months. That made it more digital, more convenient to use on a base ten system. However, if I divided the year into exactly twelve months of the exact same length, they would switch months in the middle of a day. Although I like the idea that time might be measured in a base ten system, having ten months caused more problems than it fixed.
Then there’s the issue of the day. I have spreadsheets worked out with a twenty hour day. That makes the analog of an Earth hour to a Kingdom Come hour close enough for comfort. It also makes it easier to use digital, base-ten time. However, lately I’ve been looking at clock faces, and understanding why our ancient ancestors decided on a face with twelve hours. It divides easily in halves, thirds, quarters, or even sixths. Likewise with sixty minutes in an hour, and seconds to minutes. Sixty divides easily into halves, thirds, etc. and superimposes itself over a twelve hour clock. We have expressions such as “clockwise” and “He’s on your six” and “It’s straight ahead, but slightly left, at about eleven o’clock.”
If I divided an hour into one hundred minutes (likewise seconds to minutes) then it would not superimpose itself onto a twelve hour clock, but it would fit with a twenty hour clock. However, the twenty hour clock (assuming ten hours in the AM and ten hours in the PM) doesn’t have the kind of symmetry as the twenty-four hour clock.
All right… now I’m also questioning the idea of AM and PM. Really? Why do we have these? An ancient human may have found it convenient to say “two hours after the sun is at its peak” but that doesn’t mean much today…
So far, in my WIP, I’m avoiding ever saying “twenty four hours a day” or anything else that specifies time. There are enough other things to worry about and keep track of. But for my own benefit, I need to make a decision and stick with it for the sake of consistency.
There are only a few days left in December. I’m at 132,000 words in my WIP which is my NaNoWriMo novel. Instead of being one novel in two parts (the first part takes place on the starship on the way to Kingdom Come, the second takes place on Kingdom Come) I think this will be two novels that are definitely a pair. A person could read the first one and then stop… it has an emotionally satisfying ending, but I leave a shadow of doubt in that ending. The second book is definitely a continuation of the first. A reader would not be able to enjoy it unless they had read the first one.
I need to finish this up soon. Hopefully before New Years, but most definitely before I start to teach in the Spring. At least this year my kids are both in school full time. Fortunately, the words are coming to me fairly well now that I’m almost done. I just need to simplify some things so it doesn’t end up being 300,000 words!
My working title has been A Brave New Whirl but now that I am splitting it in two, I will call the first story The Jubilation of the Southern Cross and the second book Hearthsong. The first is the name of the starship. The second is the name of the duchy on Kingdome Come where the story takes place.
AmyBeth Inverness 
Looking at lists of divisors such as http://primefan.tripod.com/Phi500.html, there aren’t many options. If you want quarters, you need a timebase with 4 as a factor. If you want thirds, you need 3 as a factor. For both, you need 12 as a factor. If you want something different from 12 or 24, it comes at a price, generally a tradeoff between math with larger numbers (like 60) or an awkward lack of small divisors.
If you want the half day evenly divided by 4, to get that clock face symmetry you alluded to, you need a timebase with a multiple of 8. Excluding 24, the most convenient ones are 16 and 32, which preclude taking thirds. Do you need thirds? Probably not. Do you need 4-way rotational symmetry? Probably not.
And decimal (base 10) is overrated. Base 12 (and 24) are easier, since thirds and quarters are integers.
But I’d go with 20, and get to work. Every world has a different day and year (and moons have a natural month), and no one rationally expects the Universe to make the math easy for us.
I think at some point in the story (or perhaps in another…) I’ll allude to the fact that not only do different planetary colonies keep time in different ways, but the subject is hotly debated.
I’ve also considered using a base 8, which is a perfect cube of 2 and symbolic for this world in other ways (8 moons, 8 divisions of government, etc.)