As I recall, the physics and radiobio boards are on a Thursday. I took off Mon, Tues, and Wed to study. I probably began studying in earnest 6 weeks before that. I am sure that I could have gone over the material another couple of times, done some recalls, more RAPHEXs, etc. if I took more time off, but I did just fine on the exam itself, which I found to be very fair (not easy, but fair).
As for studying, you should began about 4 weeks before the test, with 2 weeks of hardcore studying. It should not take any more time than that.
I would echo the timeframe above for study. About 4-5 weeks of serious studying are enough. What I used:
Physics
- Caggiano notes (great, but any concise review could work). Was able to get through several times
-RAPHEX (did the most recent 3 years, knowing these inside out is key, somewhat easier than the real thing but cover similar content)
Radbio
- ASTRO questions (mainly these, did last 2 years, much harder than the exam, but made the real thing seem much easier)
- Hall (i didn't read it all, was mainly my reference source while doing ASTRO questions)
The exams were very fair, doing lots of questions are key. Did not seem to be a lot of calculations this past year, know the main concepts, RAPHEX is good for that.