I cut all of my clutches on day 55. Sorry...I can't wait any longer to see what's inside. They tend to start pipping on day 57-58 for me. Never had any issue with cutting the eggs and the hatchlings having problems.
I cut an egg years ago on day 55 and he didn't come out until day 65! That one had me a little worried.
I should learn to wait, but it's hard when day 55 comes around.