From what I have read they can just stay in the turner if you unplugg it but there is a chance they can get hurt that way and it gets youre turner messy , So you can also take it out and place them ether on the bottom or in egg cartons.
I would say no because even if you turned it off three day before they hatch. They would have no were to stand and feet could fall between the slots. But maybe someone that has done it will let you know.
Turners are hard to clean, so I recommend you not hatch in it! On Day 18, take the eggs out of the turner, either put them in cartons or on the wire bottom, boost the humidity, and let them be. Don't open the incubator again. When they are all hatched, and we hope they will, or when you know the others aren't going to, put the chicks in the brooder.