Are there any monsters in QFG3 that only come out during the day? Or only at night?

Nope, I have encountered all monsters at all hours of the day.

What DOES determine what monsters you meet is what screen you're on.

Tarna and Simbani: Crocs, Giant Ants, Dinosaurs, (and rhinos, if that counts)
Giant Tree: Crocs, Giant Ants, Flying Snakes, Leopardmen
Waterfall: Leopardmen, Apemen, Demon Worms

Also, what screen you're on is what determines just how many royals you get from killing humanoids. First screen gives the least potential for royals, last screen has the most potential. Though it does fluctuate wildly.

This does mean that jungle crocs are, on average, richer than savannah crocs :>

Earth pigs only come out at night. They've been known to bore many an adventurer to death.

Boar them to death, you mean. :)

Holy hell, someone else who hates him.

Hooray!

(though I know I'm the only one that's not fond of the farmers from Quest for Glory 4, even with the improvising)

I'm not crazy about the Earth pig either. But as long as you don't sleep in the savannah, he is easy to avoid

I can relate to that feeling in a way. I'm the only person who considers QFG1 to be my least favorite game in the series (I love it I just love the other 4 games even more) and prefers the AGD Interactive remakes of all the games that they remade over their originals and any other remake. I also seem to be the only person who doesn't like LateBlt and hercrabbiness. I watched their LP of QFG2 and I hated it.

I wouldn't say I hate him. However if Arne Saknoosen's incredible reflex action ever failed him and he wasn't able to narrowly avoid an almost certain death from the attack of a violet Giraffe, well I wouldn't exactly shed any tears.