At the moment I do cardio every off day and post workout besides after legs. So 5-6 times a week. PWO is 20-30 minutes and nothing too crazy, today was 3.8 MPH at a slight incline. Off day cardio is 30-40 minutes and is done at a pretty fast paced walked(compared to other people at least). I do this for two reasons primarily, number one is for control over fat buildup as I try to gain size and two the cardio in the morning stimulates my appetite all day.
I touched on this in another thread briefly but I would rather eat extra food and ensure growth and take care of the possible loose ends with cardio than eat less and maybe miss out on some lbs gained(over long periods of time obviously).
That's how I do it but keep in mind I'm not trying to lose bodyfat, just trying to keep mine in check as I grow.
PS I hate cardio so much and have a 5 minute debate with myself everyday on whether or not it's worth it ha.