Ironman 70.3 Galveston

I am getting a lot of information about training etc. I have people that tell me that I need to swim bike and run 4x a week. In a perfect world where I don't have to work, that is possible, but I am strapped for time. I know the work and time this involves, but I wanted a no frills straight forward training program. Fortunately I have weekends off so I can afford my long rides and long runs. My weakest is the bike due to the time constraints. It's much easier be able to swim and run since you can pretty much do either one in the dark or when its wet outside. I read about doing bike workouts on the trainer, but not just to spin a little but were talking a workout on efficiency intensity hills (its all flat here) and intervals. I was planning on doing it outside where I can feel the wind heat and humidity. If I do the trainer workouts 1 to 2 x a week and do my long rides Saturday's is it possible for me to finish my first half ironman in 12 weeks? Morning rides during the week are our of the question. I also have been reading on "be ironfit" by don fink and following it until the half ironman. I like his philosophy of efficient training. It's all about quality not so much quantity. I was gonna tweak it and use the just finish and intermediate program based on my needs. Has anyone have any success in using his program? I'd really appreciate your input. Oh by the way I have been a triathlete for 2 years. Within those 2 short years, I have done 5 sprint tris, 3 half marathons, 3 duathlons, 4 10ks and 5 5ks so i am in decent shape.