How long does doughnut dough need to chill? What is meant by "chill over night?" 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.