The Scholarly Concentrations is basically a "project" that all med students who matriculated since last year are required to do. I guess you can sort of equate it to a "minor" from undergrad. There are about 6-7 areas of "concentrations." I remember Women's Health, Immunology, Molecular Biology of Disease, Bioengineering, Independet Design (basically, design your own Concentration), and a few others that I don't remember because I wasn't interested in them. When I went to my Stanford interview, they were basically saying that it might take students about 5 years to finish, but it isn't directly correlated to their introduction of the "Schol. COncentrations." It's more because Stanford Med encourages their students to take their time, and to do as much exploring of their interests as they can during the medical school years.
If you are doing a dual degree at Stanford, MD/MBA, MD/MPH, MD/PHD, your dual degree is more than enough to fulfill the scholarly concentrations. Again, depending on which concentration you eventually chose, you can be taking extra classes (Women's Health), attending a series of seminars, doing bench or clinical research, etc.
The other thing is that if you decide that you don't like the concentration you are doing, you can change it. I think most med students decide on a concentration by the end of their first year and start working on it that summer and through second year. Alternatively, others wait until they are done with all four years of med school, stay as a fifth year as a teaching assistant or research assistant at Stanford (and get PAID very very well, as compared to other TAs at other institutions), and work on their concentrations at the same time.
This is really really basic, but I know that before my interview, I was able to find very specific details about the concentrations on their website. They have a section about curriculum, and you click on each concentration and they give you guidelines for each one.
Good luck.
(I loved Stanford, btw.)