30min of directed moderate exercise a day.  That's a minimum.  That's also where the steep line of increasingly lower mortality begins to be less steep--the difference between exercising 0 min a day and 10 is huge, 10 and 30 is still really big but not a s huge, and 30 and hour is quite modest, if the point is health/longevity. 60min of active play is about the same as 30min of directed exercise.