If you do it right and don't attempt a stupid crash diet or something, you should lose 1 to 2 pounds a week. That is what is recommended. I always want to lose more but honestly, it never works out and you'll suffer for no reason. Just work out 60-90 minutes a day (making sure your heart rate is at the right rate for your age) and eat less calories than you burn. Only a few hundred calories MAX though.
Not long at all if you're willing to put in the effort. Whilst exercising, it is a good idea to take measurements instead of weighing yourself. Excersing causes you to build muscle mass whilst losing weight, which can be discouraging when you hop on the scales!
It is best to eat 5 - 6 healthy meals a day and exercise for at least 30mins a day. Walking is great. Don't go into it too quickly though or you will burn yourself out!
Have five to six small meals in a day. Cut off sugars and carbohydrates. Eat more protein rich food. Like chicken, fish, egg whites etc. But remember you need to workout as well. Aerobics or dancing is the fastest ways to lose weight. 1 hour exercise daily. It could be cycling, jogging, or aerobics. I mean cardiovascular exercises.
Don't skip meals or else you will gain weight instead. Eat healthy. Lower down your carbohydrate consumption. Intake more proteins and fresh fruits whenever you feel hungry.
You will see the results soon. Believe me. I have lost 30 kg of weight thats about 66 pounds in about 8 months. So I am saying this all by my personal experience.