Okay, I've been writing this thing for a while, and at first I was coming up with my own measurements of time, such as fictional names for months derived from our own (like Janus being January, Febras being February, etc.) I didn't refer to Spring as Spring, my characters refer to it as the "growing season" because, as is eventually revealed in the story, my characters aren't very educated. But there-in lies the inconsistency. The narrator knows how far a mile or a kilometer is, but the characters don't. The narrator knows that a week is seven days, and a month is a month, but these characters don't have that concept of time. It was once part of their culture, but in the centuries since the collapse of civilization, their particular culture has dismissed all these things and now refer to years as "cycles" and don't really have the concept of hours, just morning, midday, evening, night. But in my narration, I've been trying to avoid referring to distances, instead saying "half a day's walk" and such, but there are some things I feel like I have to put in modern day, normal terms, or else the reader might not know what I'm talking about. For example, I'm saying that a cliff is a hundred feet high, despite my characters not having "feet" as a unit of measurement. I feel like if I say something like "a hundred foot-lengths high" it would sound dumb, and that I might be underestimating the reader. Am I overthinking this?
I think it's fine to use regular units of measurement. Your entire novel is (presumably) in modern English. Are you switching out words for everything? Cats, apples, trees, the moon, pebbles, fountains, donkeys--you name it, the fantasy world presumably has it's own word (probably more than one) for it, and you're nevertheless presenting it in modern English for the sake of your audience. The only exception I'd make might be for perceived anachronisms, unless adequately explained, so that you don't throw the reader out of the story puzzling over something like that.
Just my 2p... For me, things like time, weights, and measures fall into the same bag as the reasoning I use for writing a story in plain English, even when the context of the story makes it clear that they would be speaking anything but. We still write it in English because the audience is expecting to read English, not to take a language course prior to engaging your story. Same thing with all the funky grunks of the fleck, which occur twice every floral waxing season, which are further subdivided into.... The reader has to be able to make heads or tails of what you write. When you remove the reader's footing concerning such fundamentally basic items, lines of comprehension and attention span get crossed. Another example: We don't question Sam's love of po-tay-toes for a second, though potatoes are not remotely native to Europe or Middle Earth. By the time Tolkien wrote his magnum opus, potatoes were well entrenched in European culture, but not a single European had even lain eyes on one until the latter half of the 16th century. Prior to importation, they were only found in the Americas. But again, we don't question this because who even cares? How is it relevant? Does the removal of the anachronistic potato improve the reality of Middle Earth?
Yeah, it's not high-fantasy. I still have rabbits, horses, etc. The only reason they have these rudimentary descriptions of time and distance is because that knowledge has degraded over time (but we as the readers know better). I agree, and I think having to stop and explain every tiny made-up unit would probably make the story worse rather than just saying "he waited for three hours for the messenger to arrive". Like you said, who cares? The irony is that potatoes actually play a big part in the early story (it's one of their main crops, because vodka lol)
I feel like whatever you choose, it has to be consistent. So if you choose to describe things in modern day terms for the audience's sake, that you go back and pepper it in or else the readers will get a, "And so the writer chose to give up on explaining it this way a third into the book and that style of writing was never seen again," kind of vibe. You can try and go with the flow and not explain at all the new verbage and hope the reader picks up on what you mean, provided you add a lot of context clues. Before I knew what Fallout was, I accidentally read a Fallout book and I had no idea what was happening -- what was a cap? Why are people trading it in? What's a pipboy? What's a buffout? -- but because the writing was so good and because of well placed context clues I quickly got the idea: a cap is bottlecaps people in this post-apocalypse world use to trade for stuff because paper currency wasn't feasible, a pipboy was a computer device strapped into people's arms, a buffout is a drug people use to strengthen themselves temporarily; I picked this up without having it explained too much so, you could probably do it too. Instead of 'hundred foot-lengths high' you could probably describe how the character feels about the height. Characters that aren't well-educated in books usually have a greater sense of imagery/visual-related memory to make up for not knowing how to read. So like, "The cliff rose into a pointed tip so high that even when Mark stood at its peak he could hear the water slapping against the base but could scarcely see it, or the large, pointed rocks he knew to be at the bottom." (Bad example, but you get what I'm saying. It communicates that the cliff is high without ever needing measurement.) Good thing to note is if you think you're underestimating your reader, then rework what your doing and get a second opinion. Hope that helps.
As long as it's well established early on that the characters refer to measurements of time/weight/whatever in such a way, there shouldn't be any problem. I think it presents opportunities for creative use of language in describing things within this framework. If you treat it like it's a normal thing within the world and you play within the rules you yourself are establishing, I think most readers will accept it and play along. The problems come when you establish the rules, and then break them without rhyme or reason.
One thing I read about J.K. Rowling and one reason why her writing was effective for many readers was that she established certain key phrases for each character that would allow the reader to know who was doing what without ever referring to them by name just by the identifying phrase. If DPena were to do something like that, early on using a few concise phrases in conjunction with audio/visual descriptions or strong character reactions, then for the rest of the book DPena could simply use those established phrases to summarize the measurements in question. He/She might have to periodically pepper in descriptive prose to reestablish/reinforce what these phrases mean, though. Thinking realistically, no society (regardless of how primitive they are) would have to have some sort of agreed upon common descriptor for such important things as time/weight/other measurements. These types of descriptions are critical for survival, not just a modern convenience. Even if society were to collapse and centuries pass, new phrasing would arise (probably bastardizations/corruptions of existing phrasing). Without this type of vocabulary, a society can't function in a cohesive manner.
It would not sound dumb. Why? Because the "foot" is exactly what it sounds like. The average length of a man's foot. Just like how a span is the average distance from the tip of your little finger to your thumb, a cubit is the length from the tip of your middle finger to your elbow, a tun (not ton) was the amount of liquid that would go into a barrel, a stone is the weight of a "standard" stone and so on. These are "natural" units based on the things people used in everyday life. The actual measurement varied from place to place, but approximated to more or less the same measure. As long as the characters in your world have feet, there is no reason why a foot would not be a measurement.
I would also use natural measurements for most things. I see no reason you can't use feet to describe the height of a cliff, but perhaps they might use something else. "100 feet" is fine, but you could also describe it as "as tall as 20 men" which is about the same height. Maybe read some stories from ancient cultures that didn't have precise measurements like we do. Homer comes to mind, and he measured things by comparing them to other things. For example, the sea monster Charybdis's measurements are left vague. There is no reference to any unit of measurement of the day, but you are given the information that it's no wider than the range of an arrow. I don't really know much about greek bows, but it gives me an idea of maybe 20 yards, which if described that way would just diminish the impact of the creature. He also described the great wooden horse as "mountainous" in size, which just provides an abstract concept of being really big. You're also told they dismantled multiple ships to build it, so you have an idea of it's mass. You also know that it can't actually be all that big in modern standards because it actually fit through the gates of Troy, so it couldn't have been wider than like ten feet and no taller than it's walls. I do have an issue with referring to spring as the "growing season." Have you ever grown a garden? If you told me something happens in "growing season," I'd very much picture summer, not spring. Maybe call it "planting season?"
