I too remove them from the turner any time day 18. Technically they don't need turning after day 14 as by this stage in incubation they should have formed their body parts in the correct position. But many/most find it good practice to continue to day 18 and stop turning at lockdown when the humidity needs to be put up to a higher level for hatch.
Good luck with your hatch and enjoy your time here on BYC
Not sure if it's "good practice" that people wait until day 18 or 19 to take the turner out or it simply works better as that's the time you're upping the humidity so why not wait as it doesn't hurt anything.
If you have a turner that stands the eggs up and tilts them back and forth, the advice in the above posts is valid. If you have the kind of turner that lays flat on the floor of the incubator and rolls the eggs back and forth, you don't need to remove it, just unplug it and it becomes part of the floor.