The impact of the calories you’re expending will depend on the calories you’re taking in. If, for example, a diet of 2000 calories is what it took for you to maintain your weight, you would need to other EXPEND some of these calories to reduce it and lose weight, either by eating less, or increasing exercise. 609 calories is a particularly large amount of calories to burn, so I can only imagine you’re on the right track. That said, be careful not to OVERDO it either! When you train for over 60 minutes at a time, your stress hormones are called to action, limiting the effects of your workout, and precious muscle mass is also burned. I would stick to the shorter workouts as a regular rule, and make sure you are supplementing correctly during the 90 minute workouts.