I transitioned for over a year but not on purpose. I got my last relaxer near the end of 2001 and started wearing microbraids, cornrows, weaves, etc because I was tired of sitting in the shop all day on Saturday for my new growth to barely get straight any way. In August of 2002 I decided that I wasn't going to get relaxers any more. I got trims and deep conditioned every 4 weeks from late 2001 to March or so of 2003 when I decided that I didn't care how long my hair was I was tired of the braids and all that.
My hair was just below my earlobes when I started to transtion and it was shoulder length when I got it blow dryed/flat ironed for the first time in August 2003. I never did a BC but at the time I thought my forehead and head was too big for short hair. If I could do it all over again I would have done the BC vs. wearing the braids because my scalp suffered.
I would say it depends on your comfort level with the length of your hair and knowing that you will have to baby your hair because of the two textures. Personally, the right time to do the BC is when you are tired of dealing with the two textures and/or when you are ready to see what your curls really look like.
Relaxer free since 12/2001...
Mostly 3c with 4a in the back.