I definitely think that it's at least somewhat specialty driven. I'm going into peds, and a lot of places interview 3 or 4 days a week from November to the end of January...That's a lot easier to schedule than the Ortho programs who have maybe 5 interview days TOTAL out of the entire season.
If you're going into an easy to schedule field (peds or medicine), December might be feasible. Otherwise January is probably a better choice.
Also, always wise to talk to the fourth years at your own school.