What FFF said x1000.
It's not too difficult to bash out four hours a day, but four quality hours per day is another matter. You can make your eight days as easy or as hard as you want to, but you'll only get out of it what you put in. My vague (alcohol clouded) memory of training was that two or three hours per day was comfortable. More than that and I started making mistakes. Sure, instructors can fly for many more hours per day, but when you've reached that level of proficiency the flying is the easy part.
Oh, and don't forget the value of interspersing your hour building with the odd instructional flight. Hour building without guidance can allow you to cement bad habits.