How quickly will child protective services investigate a home?

My sister in law is going through a nasty divorce. She is making a phone call this morning to child protective services on her soon to be ex because he is living in his mom's home and taking his children there during his parenting time, and the home is absolutely disgusting. To the point that it should be condemned. Animal feces and urine all over the house along with at least 15 cats and dogs. When he takes his 5 and 6 year old children there, they are confined to one room where the animals are not allowed. They sleep on the floor on sleeping bags, and have to use a baby potty and cannot be bathed because the bathroom is so unsanitary. My sister in law does not want to take the children away from their father, she just wants them to be in a clean, safe environment, and since he continues to take the children to his mom's house after she has repeatedly asked him not to, she figured this is the only way to keep them out of that home, and force him to spend his parenting time with the kids in a better environment. So the children are scheduled to be with their father this weekend, and she wants to know if making the call today is soon enough for child services to investigate before he picks the kids up on Friday.