Bummer that you need surgery. But it’s a pretty minor one normally. So, good luck with that. Being in a good shape before the surgery will help you recover faster. Listen to your doc as to his recommendations for returning to training afterward.
You are being smart to get started ASAP. As for where to start when you get back at it. That is a good question but not one that has an easy answer. For the aerobic training I’d suggest starting back at the volume you were at 3 weeks before the surgery. You’ll have to be aware of how your body is responding to the training. For strength. You’ll be in the Max Strength phase then and you’ll need to assess how much you have lost in that time. But you’ll figure that out fast and you’ll regain that strength in a couple of weeks.
There is no way to advise you what a reasonable volume for week 20 will be. That is just too far in the future. I could not plan that far away if I was coaching on a daily basis and had done so for for years. There are too many variables involved to plan that far ahead. From using the book you should know that this is more art than science and general guidelines and basic principles are what you need to use for guidance. Do not get too caught up in the minute details or you might miss the big picture.