I use a sportsman bator, on day 22 i break open the pipped eggs. I just cracked open 3 eggs on my guinea eggs that I had in bator. And they are doing fine. Got 20 so far LOL . Humidity and heat are the key factors for a good hatch.
hay will rot and get a rotten smell. Straw is what most farmers bed with, straw is hollow and allows moisture to soak in unlike hay. But I do use grass hay in the nesting boxes, they dont seem to scratch it out as bad. Seems more natural to them I think.
Hens are picky, Ide check them once or twice if you'de like, a day. But make sure you do it at the same time every day. they dont like to be disturbed.