pip waiting game

how long do you have to wait before you know that the egg that is pipping is either going to still come out or if its dead already inside the egg. i have 15 eggs 3 are clears so there out now 12 left 3 have already hatched out and still have one that has been pipping sence may 2nd at the night time is when i think it started and it is still inside the egg and i dont see any movement or anything. could the baby be dead already or what and should i help or let nature take its own course and let it come out if it wants to come to the world? Please help me with this problem. thanks.....