It depends on the person. Some people cant handle the 2 textures and big chop right away, some people transition for years.
I started my transition back to my natural hair in Feb 2011. At that time my hair was past my shoulders. About 10 months into my transition, I went for a trim and told my stylist to cut a little more than a trim, so I ended up with my hair to my shoulders. After that I just cut off some ends every few months till they were all gone.
Next month will make it 2 years I havenít permed my hair and I couldnít be happier with my hair.