Need the heart Rate up for max/best effect of cardio.
I know a guy that goes between machines doing light lifts for 20 min's non stop for hit cardio. Cardio can be anything you can do STEADY and at a higher pase for 20-30 min's. I used a Hand Bike. With it not running or leg work does that not make it cardio? NO
Anything done to burn fat is cadio, how much time you want to put in for results depend on what you do.