When to take biddies from the hen ?

I had a chicken to start nesting in my horse barn, not my chicken just happened to like my place I guess. Anyhow she laid 17 eggs and started sitting on them. Now all of them hatched out successfully. I noticed my cat was watching them right after they were born and decided to build them a coup to protect them. I put the hen and biddies in the coup with starter feed and water. Its been 3 days since they hatched and was wondering when I should let the hen back out and raise the babies in the coup without her. I tried to find the answer by googling to no avail.