if you want to lose 8kg with a healthy way, it will take 2 to 4 months. you have to eat healthy an avoid sweets. do cardio and exercises. You can lose 8kg in 1 to 2 months with a starving diet and a lot of cardio and exercise. but if you do the unhealthy way, when you lose the weight ,you 'll start eating more and you'll get back all that weight or more. remember tha healthy is to lose only 2-4 kg in a month and not more!!
That would really depend on how much effort and determination you'd put into your weight loss plan. The more effort and determination, the faster you'd reach your goal..