More is not better; and 30-60 minutes is about right. If you have a lot of fat to lose, I recommend getting a cardio session in at least 5 times per week. If you don't have much to lose, sometimes doing cardio on non-weight lifting days is sufficient. Each of us is different.
If your diet is clean and you are doing cardio a few days per week, yet, still not losing fat, you know you are either eating too much of the wrong foods or you need to increase the calorie burn through cardio.
Beyond an hour of cardiovascular movement, most people begin to reach a point of diminishing returns, over-training, and adaption. Remember, once the body adapts to a stimulus, have it be weight training or cardiovascular exercise, you will get little positive response of your body from the exercise.
Plus, if you are able to perform the cardio exercise for more then an hour, chances are you are not using enough intensity throughout the exercise. Low intensity, long duration exercise is not the key to success with fat loss through cardiovascular exercise.