All you can do is give it a try. I'm not sure how they will take to it...if they have no alternative and are shown where the heat is, they might be able to use it well. I had to show Scout - once - but he was used to being under Mom so the dark didn't bother him. These new guys taught themselves for the most part. They change so fast as chicks - daily more than weekly. So I would think that the sooner you get them started, the better off you'll be. I'd also set it up early in the morning so they have all day when it's light to explore it and figure out that it's warm in there. Good luck!
Thanks!