no! it is better to do the 30 mins. Even better is 40 mins like 5 x week. I do 40 mins 6x week. See, when you exercise your heart rate goes up and for good quality aeorbic exercise you should keep that heart pumping for at least 30 mins. Any more exercise than 30 mins and your body will have used its energy (from your food you ate that day) and will revert to using fat from your body. So keep up the good work!! Its hard to do that 40 min but when your done you will feel great! Keep going! LIZ