Considering your intent and willingness to get thin,you can achieve your target in 8 weeks.Ideally it is always said,one should exercise as long as it doesn't become an overdose and strain oneself.Generally an half hour of regular exercise at your gym should be enough.
If you plan to do more then do take a break of 5-10 minutes in between sessions. Also a good 15 minutes of walking or jogging or cycling in the early morning would benefit.Also remember to take good rest after a heavy workout in the gym.
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Doctors reccomentd around 30mins of excercise a day.

if you are doing cardio work (which is essentially the best excercise for weight loss) the maximum ammount you should be looking to do is around 20minutes at one time to prevent muscle loss.

YOu can calcualte the heart tate you need to be at while excercising to ensure that you are doing cardio vascular work. First, subtract your heart rate from 200, and then multiply that number by 0.75. that number is what BPM you should be at or over to ensure quality cardio work.

one way to tell is you are doing cardio work is if you are sweating by then end, then its good cardio becasue sweating is a sign that the body i burning fat in order to provide you with energy to continue excercising.