I think it is about 1/4 turn and at first when you try it could be stiff but give it plenty of oil to soak it.if you can get under put a spanner on it and try.
I can get in underneath and turn it a little (with front prop shaft removed), but it feels VERY little, less than a 1/4 turn as you mentioned. Also it is stiff, so I was just wondering what forces and travel is required before I break something