I would usually apologize if i know they’ve been waiting for my reply, or i’ve told them i’d get back to them within a certain time but wasn’t able to for some reason. But i wouldn’t apologize just for an ordinary non-urgent email, especially not after such a short period as 24 hours. But you’re not wrong of course, maybe you’re just the more efficient type who like to get things done ASAP, and that’s not a problem. :)