after waiting 4-6 weeks for most of my schools and not hearing anything, i called them. Pretty much what they said was - "we're interviewing until april, so you'll hear something between now and then" I feel like they should have some time frame, but what i think doesn't really count.
An average time would not really tell you anything anyway, just like stats don't really predict anything. A lot of schools interview the better prospects (not necessarily just based on stats!) first, so the length of time your file's been complete is meaningless unless you think you're one of their very top candidates. Patience, kiddies, patience.