It took me three months to transition to a BF running distance of 25km and 6 months to get into Ultra distance. Personally i just got rid of the bad shoes after a couple of failed attempts to mix BF with shod running. It was the right choice as far as I am concerned. I think by doing so I made the transition faster because when I wanted to run it had to be in either BF or minimalist shoes.
Another big change I made was to get rid of all my old regular shoes and get all minimalist shoes. I think this helped with improving the strength of my feet while I was just walking around, plus it was such a great feeling to always feel so connected with the ground. I even took out the inners. I went with Terra Plana as they have a good selection of shoes that you can get away with wearing to work and just out and about. Although you can do that in Vibrams you will spend a lot of time answering questions about the Monkey Feet.
Take it really easy in the transition, injury free running is waiting for you when you get there, but on the way, if you push it too hard, you may well really hurt yourself.