It's taken me over a year (ETA: and I'm not quite there yet) but that's due to a lot of bad practices on my hair (i.e. neglecting my regular henna treatments, not moisturizing properly, stretching relaxers too long). Lessons learned!!
Man I better get on my A-game. I want to be APL by my May 2008 graduation so I have less than a year. I just got to SL or a little past SL I don't know.
From reading the other post, it also depends on where you are at shoulder length. I'm about 2 inches past and have 2 inches to get to APL so maybe I can get there in 6 months.
I'd say a year for full, undeniable APL!!!! It'd also depends on your personal definition of where SL is. Some see it as the bottom of the neck, some see it as actually an inch or two below your actual shoulder.
I consider SL when hair reaches/brushes your shoulder. My hair is currenly collarbone length which is that 2-3 inches pass shoulders. It seemed like it took me 6 months to get here!