Interviews begin in September and generally run through May...some schools even later.
Interviewing before Jan 1 is ususally a pretty good sign. Interviewing earlier is a very good sign. Interviewing later is not as good, but it doesn't mean you cannot get in.
One admissions director told me that by February, 95% of the class is filled and they are interviewing for the last 5% and wait lists.
If you are early in the interview schedule, they are more likely to take a "mediocre" applicant, whereas later in the interview schedule, you need to really shine in order to be placed in that last 5%.
The more open spots they have, the better your shot at getting in.
Good luck.
JPH