I posted a similar topic about a week ago and the consensus was about 12-14 weeks under lights. Some are all about early, early, early, and have already started (even in areas like Chicago and stuff), but most say about 3 months or so. I went back to SilverSurfer's thread and I think he started in mid Jan or so and planted out like April. I think he was going for the beginning of April, but weather was crazy.
I am going to start come the end of January, hoping for an end April plant out.
Hope this helps.