It honestly depends on your relationship with the doctor. For example, my father's good friend is a plastic surgeon, I arranged to shadow him for 8 hours at a time for a couple weeks 3 times a week. But while interning(part of the internship allotted for shadowing hours) I could only get in a max of 4 hours a week. If you know the physician I have found in my experience and my friends' experience that it is much easier to stack hours. My buddy (who is currently at a DO) asked his mom's friend if he could just do 80 hours of shadowing in 2 weeks if he bought him lunch everyday and the doctor agreed.
Programs are usually more spread out I've found. The one we have here is 4 hours a week every week.