If you still have something for them to eat on free range, I'd let them do that. It gives them exercise so they don't get too fat. If they're cleaning it all up you're probably not feeding too much. When there's too much, they won't finish it. Also, as their nutritional needs are being met by the ff, the amount they eat will decrease so though it seems like a lot at first, like you're not really saving much, they will eat let within the first... I don't know... I want to say a month but it could be longer.