@jkent I have certainly never even heard that advice and would not have taken it if I had. It depends on the conditions underfoot, the breed, the size of the puppy (some breeds have very large ones !), off leash or regimented walking, stopping to admire the view / watch the puppy socialise with dogs he/she meets.
SO many things to take into consideration. I wouldn't pay much attention to generic advice from the KC. Our breed is 'different' !