It doesn't matter. Having shadowing experience will not affect your application to post-bacc programs.
Having said that, I think that it's a good idea to shadow physicians for your own personal benefits. Although shadowing only shows you a very small part of what a doctor's life is like, you will gain insight into what their work is like, the work environment, work relationships, etc. I, too, have volunteered at a hospital, and I will tell you that the shadowing experience is totally different. I was fortunate enough to have the opportunity to shadow ER physicians and an ophthalmologist in the OR. I loved every moment of it.
Shadow whenever you can!