I have gone for half a year or longer exercising on average 5 times a week, sometimes more. Excercise is often physically draining for me afterwards. My experience is opposite of it taking a "long time to [feel?] benefits": it just takes 10 pushups to a 7 minute circuit workout for me to feel great and invigorated. A longer workout often leaves me feeling drained in the hours after. My circulatory system might feel much better, but my body feels tired.