With all due respect, I don't think you should be asking "when to turn in for the gates." Obviously, you should turn in for the gates when it results in you being just inside of the right hand gate ball with optimal angle, speed and body position. Where exactly that turn starts (bow of boat distance to gates) will be different depending on how wide you are and how quickly you complete the turn. Some folks are successful being super wide and slowly turning in; others are equally successful with a narrower gate and a sharp turn in.
I suggest to only worry about getting the optimal pull out / turn in that results in the best angle / speed / line load / body position. Get that motion figured out first. If you do it perfectly but miss the gates early, go later next time. If you are late, go earlier. In short, picking "when" to go is the last thing to figure out AFTER figuring "how" to go. To pick an arbitrary pullout location then force your pullout and turn in to fit that location seems backwards to me. Learn to ski the line length first, then fit that motion to the gates. It might be best to practice free skiing -32, including the starts. That way you can focus on the proper width and timing of your new, shorter pendulum without having to worry about being early or late.
That said, everything Dave Miller said is correct...for him. And if you are going to try to copy a successful skier's gates, that is a great person to copy. However, I would be more focused on copying his proper width and glide, followed by copying how he moves in and carries the proper stack in perfect timing with the natural pendulum rather than focusing on the turn in point itself. That will come with experience.