On Day 18, I remove the turner and put the eggs on the shelf liner-covered wire shelf on their sides, then up the humidity and close the bator. That way, I don't have to open it later. It would be hard for them to hatch in the turner, very likely to get stuck in there.
If you mean a styro bator, it is best to remove the turner on day 18. To many spaces for chicks to get legs and feet stuck. A chick with a broke leg is hard to fix, if it can be helped at all.