Well, heres what i know:
15-30-15 is pretty good for lowryder2 all the way through.
For other plants:
Vegetative: 20,10,10 or 30,15,15
Flowering: 10,20,20 or 15,30,30
Are you talking about the shortest time, or the shortest height? You can keep your plant tied down for as long as you want and still produce massive buds. This also applies to height. As long as your plant has a lot of nodes, it's going to produce massive bud.