
8 - 16 weeks, it would only have been let out from its injections on the latter part of this, so 10 minutes socialisation on the lead once or twice a day will be enough.
5- 6 months - About 20 minutes once a day, or two sessions of around 15 minutes.
6-12 months - About half an hour or so would be sufficient.
You cannot write a rule book on this, several things need to be taken into account. Have you a garden that the puppy would be getting exercise in, if so reduce the above.
You can do lots of little training sessions at home and outside during this time. Mental tiredness is far more benificial then physical.
The important thing is not to let him have much free running during the growing period, especially with other dogs, as they do tend to go a bit mad

If he/she is a pup that is happy to trot along with you off the lead in the woods, then fine. Running around in a field off the lead is not.
As an adult, yes they will keep up with as much as you can give them, but I find routine works best, so an hours run every morning sun or rain keeps mine happy for the day.
Hope this gives you a guideline.
Sandra