How long does it take to flatten a chubby stomach?

To lose weight isnt about going on a diet, diets are short term and dont work. If you want to lose weight and get toned up and feel fitter you need to change what you eat, the amount you eat and exercise at least 3 times a week for it to have any benefit and last!
A healthy weight loss is 2-3lbs per week, and you will need to eat at least 800-1000 calories less per day in order to achieve this. But these figures need calculating depending on your body structure, height and weight as you are now and how active you are already.

Exercise wise, to help you lose weight you need to do aerobic style exercises that get your heart rate and cardio working this will speed up weight loss, once you start getting closer to your target weight then start to introduce toning methods. To get fab flat abs is very hard! and you can achieve it but give yourself a realist time frame depending on the amount you need to lose, keep at it, and dont give up.