It really depends on the incubation temperature. My eggs at 88 degrees always hatched between 41 and 43 days. I have some more info on my web page. I would not cut any windows in the eggs. This technique may work for some pythons but I have never heard of it applied to any other group. Generally if the eggs are good they will hatch. Calabar eggs that I have eventually had to cut open had deformed embryos inside. Your eggs should be close.