I like to cook my chicken bones for 4 hours in the IP and the broth is a rich brown and the bones are soft. I can’t remember how long I cooked my beef bones, I think it was 6-8 hours before I got a broth that looked as rich as my chicken broth. When the beef was done, I added more water, salt, etc and cooked them again and the next batch of broth came out just as good. I ended up cooking them three times. I found a blog somewhere that said you can keep cooking them until they are soft.