Okay, now that you've seen the previous replies, allow me to bring you back into the real world.
The real question at hand is HOW IS YOUR CURRENT ENDURANCE LEVEL?
If you are weight training for bodybuilding, then you will HAVE TO perform at least 20 minutes of cardio 3-4 days a week.
If you are weight training for powerlifting, then you should concentrate solely on weight training.
Cardio helps the blood flow faster and begins the fat burning process. Granted, building muscles burns fat 24/7, as well. But all and all, cardio gives you that "great start" before a hard bodybuilding/powerlifting workout or that "finishing touch" after the training, whichever the time you choose to perform it.
Strength training since 1985.