You get about a foot, foot and a half, sized plant at the end of 90 days.
Edit* I guess I shouldn't give EXACT sizes. They differ from strain to strain. Try it and see. Some Auto's were made for this i believe.
You probably could do it...but it seems like it would be a waste of a seed, since you wouldn't yield much from it, due to the small size. Try it and let us know...
A plant has to have a veg period, no matter what light cycle you use it will have to veg until its large and mature enough to start flowering. Your just wasting 12 hrs everyday the plant could be using to get bigger and mature faster......if your not doing like a party cup sog or something it is a total waste imo.