In complete agreement with "...once they can stand up and eat and drink...". This philosophy works with a plethora of conditions from assisted hatches to splayed leg to shipped chicks to...it's unlimited the cause but end result is always the same- once they can stand and feed themselves they are good to go.I don't think it should be a matter of opinion so much as a matter of fact.
It varies a little from chick to chick, however once they can stand up and eat and drink, they are good to grow. When there are 6 or more of them together in warm weather, they don't need any heater.
Cold weather is different, and like people, no chick wants to be alone.