Hi!
My understanding is that as soon as the higher percentage exceeds the amount you would feed as 2-3% of your puppy's estimated adult weight, you switch to that amount.
For example: A 10 pound puppy whose estimated adult weight is 100 pounds would be fed 1 pound, spread over several meals. When the puppy weighs 40 pounds, if you use the 10% rule, you would be feeding 4 pounds - too much! - because the 2-3% rule maxes your dog's "anticiated adult weight" of 100 pounds out at 2-3 pounds of food total....so when you get to the point where amount of food you are feeding on the 10% rule is GREATER than the amount of food you would feed at 3% of anticipated adult weight, you switch to the 3% of anticipated adult weight.
I did not say that very clearly! Did it make any sense? If not, tell me what kind of dog you have, his weight now, and his anticipated weight, and I will do the math for you (good thing I am better at math than I am with words!)!