if you're in a calorie defecit you will lose weight. that is the one universal truth!
i would advise doing it in a way that is sustainable for you. if intermittent fasting helps you restrict your calorie intake, then great!
900 is way too low. its unsustainable, you will feel letharic and have a low mood. you need at least 1500 or so calories a day minimum, depending on your body mass, gender and age. you need nutritious food too! fruits, vegetables, complex carbs, healthy fats, complete proteins. 900 calories of rice, crisps or chocolate is far from a nutritionally complete diet, and will have a detrimental effect on your health.
tl,dr: yes you will lose weight. this is not healthy or sustainable.