Correct me if i'm wrong, but aren't they supposed to look like that at about 40-45 days?..I have not bred BP's, but I've done ALOT of research and from my understanding they'll start to dimple when the yolk is almost gone and they are about to pip....I may be wrong or they might be more then normaly dimpled/sinking at this stage.

Either way, hope all goes all Good as possible for you and your clutch.