Double Cardio

I was thinking about doing double cardio. When is the best time to do it? Is it worth doing? How many times a week is benificial? Do I do it on days I work out? I already do cardio 4x's a week for around 45 minutes. My stats are 176lbs, 5'10 and not sure about body fat(have pic in members pic area).

whatever you decide just do it first thing on the am on an empty stomach. dont do it twice in one day especially work out days since you might be strapped for energy. does do it everyday then