No this is not true. The minute you start exercising you are on your way to burning fat. There is not a specific minute assigned to when you begin to lose weight.

Weight loss is energy put in is equal to the calories burned or gained, depending on if you have eaten more calories that day than you have exercised.

The twenty minute rule is associated with when you begin to notice cardio benefits from your activity. Doctors recommend you elevate your heart rate for twenty minutes to ensure you are working your body hard enough to give it proper exercise and access the full benefits of your workout.

No this is not a correct statement, In order to burn fat you need to concentrate on your diet, plan it carefully and follow it accordingly.Do not opt for junk food, high caloric food.Make a habit of eating vegetable salads before one hour of your meals. Reduce the quantity of carbohydrates in your diet.

The answer is no. Your body is ALWAYS burning fat! According to menshealth.com, this myth stemmed from an out-dated belief that a person "needed to exercise in a range between 60 percent and 80 percent of their maximum hear rate. Any lower was too easy, and any higher made it too difficult to efficiently use fat for fuel."

However, this is untrue. Your body uses more energy when training at high intensities so it is more beneficial to exercise at high intensities for short periods of time than for at a low to moderate insensity for a longer period of time. In short, it is about quality (intensity) instead of quantity (time). How long you exercise isn't near as important as the quality of the exercise.

All that being said, "once you've been exercising for 15 or 20 minutes, your body has made the shift to using a higher percentage of fat for fuel. But again, if you're trying to lose weight, it's about the total number of calories burned, not necessarily the fuel source."

For more information, check out my sources!