It varies widely, as others have said. Some of this variability is at the department level and some of it is at the HR level. You want to look at the timeline in which the department says they'll begin review....but sometimes it takes FOREVER to get from looking at the pool to doing initial interviews (phone, Skype) even IF a department does those, and then it can drag on from there to hear about in-person interviews. I know for my program, the ad has to be posted for 30 days before we can look at applications and then we try to do phone/Skype interviews as quickly as we can to get on campus interviews completed before the December holiday break. Which doesn't always happen, but the goal is to get offers out before the new year.