o yeah...3 weeks veg will be nice. some people veg for 2 weeks then flower...called SOG or sea of green method, some people go right to 12/12 all depends on how yyou want to do it...more generally the longer you veg, the more you will yield
I usually veg my plants for 4 weeks under cfls before flowering but my last grow I put a freshly rooted clone straight into my flowering room under my 150w HPS on 12/12 because I cloned too many and it harvested more than my others!? I think better temps and training had more to do with it though, just experiment.