To be honest with you, for most programs, it doesn't make any difference. I would refer you to an interesting study by the EM program @MSU-Kalzmazoo, published in Academic Emergency Medicine within the last couple of years. They looked at rank lists (where candidates wound up on the rank list), and compared that with the dates they interviewed. There was no corrrelation between when people interviewed and how they were ranked numerically. (I realize this applies only to EM in this study).
It's published in the September, 2000 issue of AEM, by Martin-Lee, Park, and Overton.
Hope this helps.
Marc Squillante, DO
EM Program Director
OSF St. Francis Medical Center/ Univ. of Illinois College of Medicine @ Peoria, IL