i have actually had chicks hatch up to day 22....so I give 5 days after day 17 or 48 hours after last hatch before final candling to confirm no more hatchesI think I stopped turning the egg on 14th day...and I remember her hatching precisely in time, a textbook case like, peeping at day 16.5, zipping almost exactly at day 17. I heard of chicks popping out at any time from day 15~19, so I would wait out until day 19 if you are worried that they are a little slow? Again, wish you best luck!