Northwest Michigan- When are we making babies?

We are in Northwest Michigan and should be warming up in March. My gals did great this winter and I am so excited to hatch their babies this spring!

When do northern US chicken tenders usually start incubating fertilized eggs? Do you have a preference on hatching with an incubator or letting your gals just sit on their eggs?

I am assuming April or May will be most safe when temps are above 50 degrees but unsure.