I think it depends on why you want to take it early and how you plan to study for it. I just took it a couple of days ago without having had medicine, surgery or family medicine rotations, and I felt ok about my preparation. Having said that, I took a leave of absence in January for personal reasons and have been doing nothing but studying rotation-related material since then. If you're on rotations now without a dedicated chunk of time to study the material you won't have rotated in, then I'd say it's a bad idea. If, on the other hand, you have time to do nothing but study, then sure, why not, get it out of the way.