From personal experience (but not baby chicks) I would not leave chicks on screen porch over night. Leaving them on porch would be an open invitation to a "dinner party" for the coons. Coons come in thru the screen leaving big holes and messes, they also leave thru new holes and you may never hear them. What the coons don't get the cats will. I ended up with 1 huge hole, no screen on door and several bullet (pellet and 22) thru my screen porch before stopping the coons from coming thru.