This is my simplistic view of how the double action timing works:
The trigger pushes on the hand that pushes on the ejector & ratchet that rotates the cylinder.
But before the hand reaches the ratchet, the trigger pushes on the strut that pushes on the hammer that pushes on the rebound lever that pushes on the tang of the bolt that causes the bolt to pivot and releases the cylinder for rotating.
As the trigger moves back further, the tang of the bolt falls off the cam of the rebound lever, allowing the bolt spring to push the bolt against the cylinder. As the cylinder revolves further the bolt drops into the cylinder slot, locking the cylinder. As the trigger pulls further, the trigger clears the strut and the hammer falls.
My simplistic way is adjusting timing:
a) Shorten the strut.
b) File on the cam on the rebound lever.
c) Bend the tang on the bolt.
My simplistic warning:
The problem that there are lots of constraints, and one can't put material back on an action bar or hand.
So that is why one should follow the directions in the book and go through all the tests to determine exactly what should be done first. If you had a handful of rebound levers and hands, you could go around in circles wasting parts.
New replacement parts are too big and don't work right until fitted.
Existing parts that were fitted at the factory should probably not have any more material removed.