It depends on what you feed them, and how well the water is kept clean. The better food, the better quality water will make them grow faster. As for a timeline, I can't remember.
Generally I would wait until the fry are free swimming before I tried to move them to a new tank, just to lessen the chances of them stressing out from a new environment. For the first few WC's on young fry I would use water from the main tank they came from rather than new water until they get a bit older.