I can be a bit dense when it comes to understanding simple key points. Up until reading this line, I was under the impression that the hips (which drive the shoulders) start moving to open once you get your elbow up. If I understand this correctly, it should be the other way around.. So I get the elbow out, start the chop, then engage the hips to get that late acceleration? It makes sense now; if I start my rotating the hips before the arm extends I'm at the end of the power generated from the hips and actually slowing down so it's all arm at that point. It somewhat reminds me of engaging on a push putt. When I'm on and feeling it, there is a distinct feeling where I am almost passive until the disc starts to move on it's own at which time I actively spit it out of my hand onto a conveyor belt straight to the basket. If my timing is off and I try to engage the disc prior to it's own weight shift it comes up short or I arm it and it goes right.
that is sort of correct.
the hip rotation happens in two stages. one of them gets your body opening, weight transferring, and puts you into position (aka leads you to the power pocket).
the second rotation is a bit harder to describe, but the best parallel i can think of is a baseball player "swinging from the heels." this occurs AFTER the bat contacts the ball and they break their wrists over and then pivot the hips with leverage to push the ball with the bat.
basically, the second hip rotation doesn't really apply power until you are passing through the critical point.