<p>About how many hours of shadowing a doctor, research or pure volunteer in a medical facility really stand out and make you at the "top" of the list?</p>
<p>Shadowing and volunteering aren't really quantifiable stats. It's more that they want to see that they've been done. No one is ever going to say, "we should really take this student b/c they've shadowed 8 different physicians each for 30 hours". </p>
<p>This isn't to say that you can do a single hour, any experience needs to be "significant" and there are some amounts where it's easy to say it's a significant amount and others where it's like "nice try". What those values are, and if there really is some sort of absolute threshold, I don't know. 6 months of volunteering 3 hours a week sounds a lot better than 2 months at 3hr/wk, but is three months "that" much better? </p>
<p>Research is the same way in that there's no upper limit that will put you on top. However, I'd say the minimum level is probably a summer or a semester. What's more important is what you actually did. If you just washed glassware every day, that's not nearly as impressive as creating your own project and doing original research.</p>