FLW throughout the entire swing?

[randyng]

Does it say anywhere in the book how long one should maintain a FLW? My instructor wants me to hold it almost to the finish, which is quite hard to do. It helps me strike the ball very very solidly, but it's going to take a butt load of practice to ingrain this into my swing. I was looking at Tour swings on youtube and I couldn't find anyone that didn't break a FLW during the swivel? Should I keep on practicing this or is it not quite necessary to build a solid swing?

Thanks!