I count a pip through the membrane and begin a 24 hour count before I interfere. A stronger chick is the result of a natural hatch process, in my opinion, however with marans the chicks are so large that they sometimes become helpless. Don't panic over a drop of blood, just know when you see...
Whether to interfere with the natural process of hatch is a big debate, however, I hatch marans and will tell you that many times the chick is so large that it cannot turn in the egg to zip appropriately. I have helped many hatch, and I've also lost a couple doing that. You'll have to watch...