I just finished reading a book by "Tom flowers" stating that 24 hours of light around week 4-5 of flower will cause the plant to stop maturing already existing buds (not kill or reverse them, just stop maturation). After 1-3 weeks, the plant will grow new flower sites on top of already existing buds, at which point you would revert back to 12/12. This would start the maturation process over for existing buds, and give new ones time to catch up. This technique is said to add about 5 weeks in overall grow time, but up to a 25-50% increase in the already existing flowers, and around a 25% increase in yield overall!!
I've never tried it, but just something to think about