Sorry this is so ridiculously long, but here goes:
I took off all of December and the first half of January, and did a light rotation in November. Worked well for me. In hindsight, I probably could have gotten away with another light rotation for the first half of January. If I'd absolutely had to, I could have managed doing no interviews in November OR no interviews in January, but not both (and it would have been insane travel). Wound up going on 12 altogether.
So much of this depends on your school, how many interviews you need to do for whatever specialty you're applying in, and how spread out your geographical area of interviewing is. My school gives us a fair bit of vacation time, so they really frown on taking more than one or at most two days off during an elective. Your school may be more forgiving.
Think about the nuts and bolts of how scheduling interviews works. Realistically, I don't think you can
plan on being able to do more than 3 interviews per week, especially if you want to be able to go to the pre-interview dinners. Sure, there is the occasional opportunity when the stars align such that you theoretically could schedule more than that in a week, but I don't think you can count on it happening (and it would be exhausting). And you might be limited to one or two per week just based on the way programs' schedules collide. If you take December off, which was the month with the highest interview density for most of the people I know, you've got the holiday week to consider, so let's say you could theoretically fit in 10. In my experience, a lot of the programs I was invited to interviewed on the same days, which made things harder, so I wound up having to space things out a little more. If you want to not have to do crazy things like fly from one coast to the other and back again and then back to the Midwest during the same week, that would also impair your ability to maximize interview density. So, realistically, call it 8-9 interviews in December. Schedule one or two during your hopefully light rotations in November and January, and that brings you up to, oh, let's call it 12.
12 interviews may be a perfectly acceptable number for some specialties and some applicants, but it's on the low end for others. Also, all that is based on my own experience -- different specialties handle interviews very differently. For example, some of my friends who were applying in surgical fields had some interviews on weekend days. That did not happen in my specialty. Some small programs only interview on one or two days in the whole season, which reduces flexibility in scheduling. Some specialties start interviewing later, and some earlier. Also, if you're willing to give up pre-interview dinners, you've got more flexibility. I wouldn't recommend it unless you're absolutely stuck, though.
Anyway, that's probably enough out of me. Long story short: I'd advise taking more than 4 weeks off if possible.
