I've left mine to simmer in the pot for up to 48 hours on the low setting.
This is not discussed enough - good bone broth needs to cook at least 24 hours, with what you are saying being even better.
I hear that some people like to stick the bones in the broiler to brown first. This gives it a deeper flavor. I don't use that method, though.
I like mine broiled first for the beef bones, not so much the chicken. I would love to try throwing them on the grill too, but I haven’t done that yet.