Eggs really don’t need to be turned after about 14 days of development. You can take those out of the turner and remove the turner. We normally stop turning when we raise the humidity and go into lockdown more from convenience than anything else. Turning them won’t hurt them but it’s really not necessary.
Not all eggs hatch at exactly 21 days. Lots of different things affect that, heredity, humidity, how and how long the eggs were stored, and just basic differences in the eggs. A real big factor is average incubating temperature. If the average temperature is a bit cool, they can be late. If it is warm, they can be early. When I first got my incubator I had eggs pipping when I went into lockdown. It was running too warm. I tweaked the temperature and got it to perform more like it should. I still occasionally get hatches two full days early, both under a broody and in this incubator, but I also get most to hatch about on time. Each incubation is different.
What I suggest is that you go into lockdown mode immediately. Get that humidity up and prepare yourself for an early hatch. That chick is positioning itself for internal pip or maybe for zip. If you tap on the incubator it may peep in answer. It should get exciting soon. Then when all this is over, calibrate your thermometer to see if you need to lower your incubation temperature a bit.
Good luck on the hatch. My first really early one was still very successful.
