Okay yes, lmao, you're the only person who got the point of my post.
I think fandom spells like "tempus" disregard the hypocrisy of the wizarding world. Magic users are sooooo annoyed by Muggles but they adapt Muggle inventions all the time--the Weasley family clock, The Knight Bus, "spello" tape, wacky elevators, etc.
I don't know why it still sticks out to me, but there was a scene in either the first or second Fantastic Beasts movie, and they were like, setting the table for dinner, and it was all "magical" and "fantastical" in they way they levitated all the food and cutlery and whatnot, and it really annoyed me! The filmmakers were like, "Look! Look! They use MAGIC to do stuff that us real people would have to do by hand!" It got SUCH a big eye roll from me because it assumes that Muggles should be jealous of witches rather than the inverse that the magical world has to borrow ideas from Muggles and then adapt them rather than having an original idea themselves.
Anyway, I think there's a lot of stuff that magic can do, and sure, there's probably a spell that tells times, but...what a weird step take as a writer to make someone cast that type of spell. Clocks are world-building. Watches are world-building.
If it only matters what time it is and not the world-building, you can just say, "It was eight o'clock." We don't have to see HOW the character found out the time--as readers, we can assume there's a clock or watch somewhere. And if there IS NOT a clock or watch available, that's actually notable!
As I write this, I'm realizing this is a probably filtering thing. Emerging writers (and sometimes also experienced writers, cough cough) have this tendency to write something like:
"Harry saw on the alarm clock that it was half-past seven."
"According to the alarm clock, it was half-past seven."
The first example shows Harry + Harry seeing something + the reader finding out what Harry is seeing--that's filtering. What we see is filtered through Harry before it gets to us.
The second example makes the reader and Harry experience something at the same time. It immerses the reader. It also demonstrates trust in the reader since we can trust the reader understands that Harry is looking at a clock even if we don't explicitly say so. The first example, however, reminds the reader that we are not Harry and we are seeing through his eyes. It can break the flow and immersion of the narration if used too frequently or inappropriately.
Okay, so what does "tempus" have to do with this? It demonstrates that the author wants to tell the audience what time it is, but does it without considering characterization, the overall world, and/or without trusting the reader. If tempus is a completely ordinary spell, you still do NOT need to tell the reader it was used UNLESS it is pertinent to the story (plot/characterization/world-building).
Let's say that the tempus spell really does exist but we know that watches ALSO exist. Turning your wrist or looking at a clock is still faster than casting a spell--AND, you can't even cast that spell outside of school until you're seventeen. (If you're home from Hogwarts, you're not gonna wake up on a Saturday morning in August, wonder if it's early enough to sleep another hour, go downstairs, find your mom, ask her to cast a time spell, and then go back to bed if it's only six o'clock.)
Okay, so we know that clocks and watches exist and are more energy and time efficient in actually telling the time. Okay. So if someone is CHOOSING TO USE A TIME SPELL, it should indicate SOMETHING. Maybe the person's watch is broken (this actually happens to Harry in GoF). Maybe they woke up in a dark room with no clocks. Maybe their beloved heirloom watch is missing. Maybe the pale patch of skin where the watch usually is makes the character suddenly very sad and in order to shake the feeling, they tell themselves they don't need a watch anyway because they can use magic to tell the time... Sure.
But let's be honest--you can literally just write, "It was a quarter to midnight" and I doubt anyone is going to be like, "PROVE IT. SHOW ME THE CLOCK."