I Got my introduction to the system in Spring '01 when I first ordered the tapes (at that point I was already a Nidan in Nahate Goju), and I watched the whole system several times from white (orange, actually) to black. I also practicing what I was watching on and off.
I didn't start actually testing and getting feedback until early '05.
So I have either been studying the IKCA material for six years or three...but I'm still only a blue belt - I hope to get a green test in before spring!