As Michael said "Overnight is perfect. 24 hours is good." I have not tried anything shorter then 12 hours (overnight) so I will take Michael's word on it. I like to introduce a new queen late day while the foragers are out or first thing in the morning after the foragers have left the hive.
Or to put it another way - while the entire colony is not at home. I also do not like putting in new queens in in the heat of the day so the bees can except the queen and not have to fight heat or other bad weather. I also feed the new hives. (My2 cents) -Mike