October Novel Prep Challenge

Sometimes, on a show like Star Trek, the human protagonists will meet an alien for the first time, and the alien will say something like, "You have 30 of your Earth minutes before we blow up your ship."

Even granted the magic of the Universal Translator, such lines of dialogue always make me cringe. But they're included for a reason: If they said "you have 30 qalods," you'd have to have some way of explaining to the audience how long a qualod is as compared to terrestrial timekeeping conventions. "30 qualods? How long is 30 qualods?" "43 minutes and 32.4 seconds." "Oh."

All of this is to say: there's wide leeway in referring to these things, but ultimately it's written for a human audience, and it needs to be understood by them -- unless, of course, you're just going for mysterious alien incomprehensibility.

Different planets will have different daily and yearly cycles, and one can imagine fantasy worlds where those might not even apply. But your readers are used to 24 hours in a day and roughly 365 days in a year, and a second is a second.

That's my take on it, anyway, as someone who has read fantasy / sf for most of my life and occasionally writes it.