My answer : it starts at the Release Point (which is variable)
Slightly longer answer: and ends at the beginning of Hinge Action.
For me- It starts as a "assembly" roll down. my words not HK- to me that part is a much slower roll and DOES NOT effect the wedges.
I feel likie I am in selected hinge as I get to shaft parallel to base line.
And I come out of hinge near both arms streaght - I say near because I dont force it into steer- The finish swivel is exactly as U say- For me.
Or if you prefer a really longer answer with some patented rambling:
Same with Finish Swivel:starts where Hinge Action ends and finishes with the ..... wait for it... Left Hand on the bottom of the plane / right hand on the top assuming a V/V grip type.
This sounds weird I know , but when Swinging it can feel like one big Roll from Release to Finish Swivel . But it isnt just any old Roll it is an Roll that has specific alignments .... which you alluded to in a previous post.
And now for some rambling:
BTW Bear you said your axis of rotation is the spine. I think there is more to the story and its a major point of departure for many a golf theorist.
In startdown , yes the tilted axis of rotation (spine) drives the Right Shoulder down plane (assuming a Turned Shoulder Plane procedure and I do recommend it) this is the period of shoulder acceleration . But there is another lever IMO. The straight left arm attached to the pivot at the left shoulder accelerates away from the pivot thereby accelerating the hands to a speed that the pivot could never achieve. The hands are travelling at faster speed than the RPM of the pivot alone would ever allow for . There is no need for a crazy drastic over emphasized attempt to spin the pivot forever with arms pinned to chest. You dont pull with arms either. You dont do that when scything grass (Wild Bill again). As such the Spine is the centre of the pivot rotation and the left shoulder is the centre of the arm swing. You can change this for putting and make a shoulder stroke with two bent arms and thereby have low point mid body. Or you can Full Sweep Release a wedge flop say and get the arms swinging early. But for full power you need a transfer of momentum and a long lever for leverage --the straight left arm and you need what Homer termed Independent body and arm motion ---one thing Lynn loves about the McDonald drills . What Abe Mitchell tried to explain in his 1933 book. Its what we do all day with our arms. Like hinged blades on a rotor .
Or one is hinged , one is a ball joint. I like your right shoulder ball joint thing. Nice.
Short version of above: Once the left arm pulls away from the body (#4 firing and its the first to go) the Arms are moving about their own centre the Left Shoulder . Well assuming a Left Arm as centre procedure ... you could use the Right Elbow as some pros do , with a soft bent left arm at impact.
A wise man once when discussing this very thing and the notion that Hogan kept em plugged in ALL THE TIME pointed me to the Augusta footage Power Golf where he is letting one rip , high and long with a driver . He is leaning back like a long drive guy , ball forward and just ripping it and almost falling backwards as he flights it high. And of note he looks like he is trying to throw his arms off as fast as he can . Sure keep em pinned for control shots with angled hinging ! Not saying you cant do that when the situation demands. As Homer might have said if he were alive to hear these arguments " The pinned arm guys arent wrong necessarily their theory is just... well , incomplete". Hogan didnt pin em all the time. You could pin em for every shot of course , not saying you cant , but it aint ideal IMO. Sure are a lot of guys doing it these days. I did for a while. with a blocked angled release. A buddy of mine just kills it like this. Short swing , pinned, sorta like the new Tiger swing. Theres room for a difference of opinion. You got options.
Let me ask U a question about EA because U have probably thought this through.
U walk up to a door that opens out- away from you- hing on left door knob on right. You reach out with your right hand to turn the knob and open the door. The question- for EA do U turn the knob clockwise or counterclockwise? 2 muscle sets. for me clockwise is good EA counterclockwise is disruptive. What do U think?