Once they are adult, its not so much a question of how much they need, but how much you can give them! They were bred to work all day in the shooting field so are capable of going from early morning to late in the day.
Have you tried doing something else with him such as obedience/agility, which not only exercises their bodies, but also their minds?
I would have thought a couple of walks a day with some free running would keep a normal pet springer in good condition. Obviously the fitter he is, the more he will want/take so as I say try to find something else to occupy him.
You could train him to 'pick up' and join your local shoot as they are always in need of good dogs and he would earn his keep too. Try to find a gundog training class in your area.