My mystery eggs are starting to pip! Could be chicken, chukar, or guinea! If you haven't already, you should check out my thread and place your bets before they hatch, lol! https://www.backyardchickens.com/t/827578/possible-guinea-eggs-in-quail-batch
Lock down is when you stop turning eggs three days before they hatch. That would be day 18 for chickens. You also increase the humidity and ensure that there is proper ventilation in your incubator. Good luck with the eggs!