Fran, the Walt Harris books are about 3Cushion. As you know opportunities to shoot for position in that game only come up every so often, maybe every 5 or so shots. This is why, I think a pro would take more time than lesser players.
Taking this argument to the game of pool, I'm guessing a Pro would take more time (on average) after the break shot than a lesser player. Maybe the shot after that, then after the 1st or 2nd ball is struck, a Pro is usually within their plan of attack, barring an unusual break layout, and then they fall into the rhythm you're describing.
I guess what I'm trying to say is in Pool (in a perfect world) the break shot is the only shot with a random outcome. In 3Cushion even if a shot is played for position and is played extremely well, a successful outcome is achieving the desired pattern(s) rather than perfectly placing all 3 balls exactly on 3 silver dollars.