wait. i forgot one thing. i was just trying out those instructions myself.
when you rotate try to lead with the elbow. so make a little bit of tension from the shoulder to the elbow. when you rotation you want the shoulder to the elbow to move together. try to imagine your are leading the swing w/ the elbow. then the elbow goes forward first. that's important. then the racquet head will kind of stay where it is since elbow to hand is very loose. it will stay where it is pretty much then as elbow keeps going forward the racquet head will flip (ssc).
loose, no cocking back the wrist, neutral position setup, rotate, slight tension on upper arm to maintain swing shape.
and you don't have to rotate that fast. just a nice turn. like in that fed cincinnati practice vid. he's doing just what i'm saying here.
Yonex VCore 100s - SW 351 6pts HL Tour Bite / Luxilon 4G 16 @ 51lbs