What is the shortest amount of time you have grown and harvested a plant and how much did you get from it??
it depends on the strain. assuming you got all the other factors (light, co2 etc) to the max. so the question probably would be more like whats the strain that flowers early and gives lots of yield?
that you can see from description of strains. if it says the flowering will finish within 55 days and you grow it half the standard size, which in my opinion is about 2 1/2 feet, you could expect something like 30 days and get decent buds. BUT, you also have to take into account the THC content that the strain has genetics for, you want to get a decent trichome formation as early as possible so you can get good buds with short flower time.