Answer: 40 days to 60 days
It completely depends upon what kind of routine you are doing and what your goals are. If you are working out on regular basis and also watching your calorie intake you can see a difference in just couple of weeks.
Keep in mind, that if you are new to working out then you are going to be increasing your overall blood volume during the first few weeks so you might not see a change in the scale at all, or a slight decrease.