They may hatch a day early. Mine ALWAYS do. So what? Remember that not all information given is 100% accurate for 100% of the cases we deal with. If you knew some of the things I have done when I started (and continue to do) you would know that everything is subject to change. Like Someone on here says "your milage may vary". (And I never actually do "lock down"....I just try to keep things as consistant as possible...I still hatched 75% the 3 times I used a 'bator) Seriously, hens do not sweat the details like we do and they have much better hatch rates...all without a hydrometer, thermometer, lockdown and such.My one worry about the D'Uccles is they have ZERO room to grow in their eggs...they are tightly fit into them right now...that is what I had posted originally and why the poster had told me to lockdown early...