it all depends on your surroundings- do you have unlimited heighth?? if yes then I would veg for abot 30 days with a flouro- thats a typical no.
If you are using a flouro, make sure to keep your plant within inches of the light.
are you going to use the flouro the whole way through?? if yes then I would suggest getting some CFL's as well.. If you are just going to use that flouro- u might be disappointed with the final outcome