It all depends on the person about how long it will take you to get through the training. Right now the wait for standz we are being told is about 6 months, but i think it might actually be a little less than that because i have alot of friends who have gotten called in for a class after just 4.
Now about your question about going 0 time to an interview, id say im going about average i came here jan of last year and im probably a month or so away from my interview. (The interviews are put in between CFI and CFII, that way if your not hired your not obligated to stay). I have had friends finish everything in 10 months though so it all depends on the person. You can do two events a day seven days a week, or one for 5 days a week, as long as you dont get behind your ok!