OK this is the first time ive used an incubator- on day 20 one egg had a crack with a hole and you could see the beak - the other eggs were making noises. this morning the egg with the whole was exactly the same with no movement or noise the hole hadnt changed and I later found out the chick was dead. One of the other eggs had hatched. I went to work and another egg has hatched. Ive got one egg where the chick has started to zip around and is making progress and one egg which looks the same as the one that died its a hole with a beak squeeking but in 3 hours its made no progress - is this normal ? and how long do I wait before internvening ?