In the recipe it says chill over night, but how many hours would that mean?
"Overnight" is just a word, not a precise cooking term, so it would mean "during the time that typical people have retired for the night". I.e. 5 or 6 hours should do it. In cases where it is possible to over-do it (like yeast dough rising), I think the upper limit would be 10 or 12 hours.
"Overnight" is a pretty lax instruction. If the recipe requires something more precise than what laymen would assume from the word, then the time would have been specified in hours.