I was listening to a podcast last week (can't remember whose, because I listen to so many), and Phil Sims was on it. He was asked very directly about this whole "he needs to sit, learn, and adjust to the speed of the NFL" argument that permeates the airwaves nowadays. He said (paraphrasing) that it took him exactly one minute to get used to the speed of the NFL. He started playing and immediately saw how fast everyone was, and said to himself, "Wow. Well, yeah, everything is faster, so I better be faster." And that was it. He also said that sitting and learning is fine and dandy, but you don't learn much by watching. You learn by playing, making mistakes, taking hits, and testing your mettle.
You know, FWIW.