This is my personal experience, so of course your mileage may vary.
They have a board once a month to consider who to call for an interview. It's usually the third week of every month. The ACP who your sponsor is working with determines who to bring to this board every month. At the board they discuss your pros/cons, and a decision is made on whether to call you for an interview.
If you never make it to this board, you will never get called for an interview.
My personal experience was:
I met the Jan board (third week); called for an interview on Feb 10th; interviewed early March.
The keys to getting an interview:
As MR Zog said, the biggest thing is to make sure you have everything lined up. If you listed three guys on your app but only two have written recs, forget about meeting a board. Make sure your recs/paperwork are tight before your sponsor starts hounding the ACP to get you an interview.
Depending on your ACP, you may have to do a meet-and-greet in Memphis before you get an interview. This is so the ACP can get an idea of who you are before he goes to bat for you with everyone else.
The way things are working right now, if neither you nor your sponsor have done an interview with an ACP then you are NOT in line for an interview.
Once you/your sponsor do the meet and greet, you can expect to meet the board the third week of that month. Expect calls for interviews to go out about two weeks after the board. After that the timeline is up to you.