um i can see a few flaws.
First you should have started your vegetative state with a 24/0 for 4 weeks+ and if your really worried about your lighting bill, once you see hints of flowering on your plant, move it to 20/4 the whole flowering stage, if your not, flower 24/0 the whole way, your plants get shorted and FATTER!!!! really increases the yield(only bt 5%)
My recommendation is 20/4, most autoflowers cant handle 24/0 aka your wasting your time trying to get the extra 5% increase in yield, its pathetic, you just have to expirement, most people cant do that though.
in 5 gallon buckets, you should get atleast 1-2oz depending on your lighting: 200w,400w,600w, or 1000w.
i recommend 600w, they almost do as much work as an 1000w.