this is my second year applying there...
if you are a very strong applicant, they will send letters of acceptance around the 15th of the month, and it will probably be atleast a month before you hear anything
if you are a good candidate, they may still not send you anything for a very long time while they review other interviewees. i have friends who interviewed early sept. and were accepted in april. the letters still come around the 15th of the month, so just keep an eye out in the middle of the month
if your interview didn't go well.... they will still take a very long time to send you a rejection... like i think i got mine in january after a september interview (they actually re-interviewed me in december, which is quite rare). the letter came at the beginning of the month, but they can be anytime they feel like sending it.
i don't really think it's as much a rolling admission process because in most cases, they will wait to see other later interview groups before considering your application.
good luck!