I was worried about this with my last batch of eggs (duck & some chicken eggs).
Every time i opened the incubator to turn the eggs, I would mist them all as soon as i was finished turning. I always kept my humidity at a constant 50-61%...but still misted the eggs every time i opened it up.
All but 2 infertile duck eggs hatched and i still have a few left that are due very soon!!
they're all growing great too!
ALSO: I kept my humidity the same all the way through hatching, and i still misted every time i opened the bator. it was a staggered hatch.