
I would only give a pup of that age about 5-10 minutes, depends a lot on whether he charges around or is just trotting with you. If charging around then one short burst would be more than enough. It is important though as you are obviously aware to get a balance so that he is not suddenly allowed freedom at several months old.
A dog of that size shouldn't have unlimited excercise until they are about a year old, build up gradually, what you want to avoid is fast running, if he is happy to trot and sniff about then no problem.
The coming back will come, work on a recall at home with treats, take your treats out with you in something you can shake when you call him. At 13 weeks he is still such a baby, you can't expect him to understand a recall yet.
Good Luck
Sandra