How long does it take to burn off weight after burning calories?

This answer is a bit complicated. First you have to understand how your body stores and uses energy. When you take in more calories than you use in a day the extra energy is stored as fat.

When you eat your body will refill it's reservoir with energy stored as glycogen. The glycogen is stored in your liver and in your muscles. When you exercise this is the first bit of energy that is used. After the glycogen is used up, your muscle energy stores are used. When that energy is used up, then your body switches to a new source of energy. Fat. This fat is broken down into energy, but it is a much more difficult process which requires alot of oxygen. That is some of the reason why your heart rate and respirations increase with exercise.

These first two sources of glycogen and muscle energy will not net any weight loss at all. When you get into the third stage of exercise fat will begin to be burned.

At this point your weight is being lost at the same exact time as the fat is being converted into energy. So this happens at the same time. Tit for tat. Weight for energy. But, you have to exercise for a prolonged period of time to reach the third stage of energy production.