I aim for at least 80% humidity, often it goes to 99% while they are hatching because earlier chicks are drying off. Since starting this new high humidity procedure, I have lost almost no chicks that got as far as pipping. With the humidity that high, it's also safer if you absolutely must open the hatcher before they are all out. No saying you should, but some late hatching chicks are saved when I absolutely must remove the early hatchers.
I recommend reading the incubation instructions on the Porter Heritage Turkey website. Turkeys are harder to hatch than chickens so conditions must be more optimal, and that's what we want for our chickens too.