Walking a dog on schedule vs. on-demand

Our puppy (11 months old border collie) seems best-behaved when I take him for a walk once every two hours instead of "on-demand." He pulls on the leash less and obeys commands more quickly. When we walk him on-demand—when we wait for him to bark—he seems more keyed-up and has a harder time staying with us and listening when told to sit. Walking him on schedule seems to work better when I can do it.