Direct one-to-one contact when I was a senior in high school--about 8 hours.
Working in a hospital as an allied health professional and having constant contact with various physicians--about 4 1/2 years
Soooo...let's hope that's good enough.
Addendum: To answer your second question, my advisor recommended that you have enough experience to know you (1) see the good and the ugly of medicine (2) enjoy the day to day activities physicians endure before you jump into this medical school adventure and (3) can answer interview questions with intelligent, truthful answers about health care.
However, with HIPPA, it's tough, I have found, to just shadow doctors at will...or find doctors, that you do not know personally, that will let you mosey around with them "shadowing" like you may want...