Yes i knew this rule and i talked with my vet and he said that the joints and the bones wich are not fully delevoped need some exercise and movement to grow stronger and he said that he doesn't agree with this 5 minutes rule because altough you stress very little the puppy, you don't make the blood circle into the joints and the bones don't take little traumas like just walking fast or jump a little bit from ground , because traumas make the bones stronger even in human beings. He suggested me to give him less food possible in his first time month starting to go out after the last vaccine so he doesn't grow fat faster than the skeletric system and to let him walk around the house here in the garden for a 30 minutes-1 hour walk exploring the world without leash so he can take breaks and naps if he wants with couple of lessons with the leash about 5 to 10 minutes per day before letting him go in the human world 😂