You can take the turner out at the end of day 18. Thats what I did. I've heard good things about egg cartons and bad things. Some chicks try to pip in the middle but can't get out because of the egg carton in there way. I prefer to put them on their sides on the wire screen
I believe the rule of thumb is if you set your eggs before noon, then you count that day as day one. If you set the eggs after noon, you count the following day as day one. So if you set your eggs before noon on Mar. 1st then, I believe, Mar. 18th would be day 18. Hope this helps. Good luck on your hatch!