This is probably wildly variable based on what kind of clients you have. I have ones that will bother you endlessly from 8-5 (charge a lot accordingly...) and ones who don't care how or when you do it as long as it gets done before launch/release date.

I like the latter the most, though one person likes to spring "hey I need a new feature tomorrow" at 3 am while they're playing wow

This also implies you are truly freelance. Not agency or studio type.