I was under the impression that shadowing and clinical experience were two separate things.
When you shadow, you just watch. You don't do anything. Clinical experience actually involves volunteering or working in a hospital, where you actually have responsibilities.
I guess some people may be more involved when "shadowing" like taking BPs and interacting with pts. But in that case, I don't think it is considered shadowing, and now has become clinical experience.
Clinical experience: Average is 1.5 yrs and a couple hundred hours.
Shadowing: Average is around 80-100 hours over several specialties (including a primary care doc).
I think under the AMCAS tab, you put shadowing and clinical experience under the same heading. But if you only shadow and have no other hospital volunteering or employment, I don't think it looks good.