I started 3 plants on a 6 on, 10 off light scheadule. All the same genetics. They usually take 10 weeks to flower. For the first 30 days, they were on the 6/10, then i went to 12/12 after the 30th day from seed. They finished 3 weeks early. 65 days total, instead of the 90 usual days. They started slow, but when they hit the 30th day with 6 more hours of light, they grew really fast to finish. Now, have some that are on day 73, and still need 2+ weeks. Same genetics. Didnt do the 6/10 on these, and seem to be back to its usual time frame. AND BOTH seemed to equal the same weight at the end. SO i thought that was interesting.
So, from what ive personal seen, 6 on/ 10 off from the start, for 30 days, significantly reduced total time by almost a 3rd. This is using GrowMau5 night puck, so keep that in mind.