[DISCLAIMER]: This information is provided as experimental data and not fact.
The only photoperiod manipulation from years of experiments that offered discernible improvements was this adjustment made for 1 or 2 calendar weeks at the point of maximum flowering rate: Daylength of 21 hours, 36 minutes with a dark period of 12 hours. To accomplish this, you need a 7 day, 24 hour digital timer. During a 7 day calendar week on Earth, the "sun" only cycles 5 times. This permits easily switching back to the regular 12/12 at your discretion. You may want to only alter during peak flower production to stimulate the plant's metabolism. Using this photoperiod throughout the flowering cycle will cause this:
A variety that takes 49 days of 12/12 to mature, won't see 49 - 12 hour dark periods under 21:36/12 until almost 10 calendar weeks have passed.
The total increase in light energy is almost 80%, which will produce larger yields, if all of your other enviromental conditions are kept optimal.
The total increase in flowering period is only 40%, half the potential room for improvement. This means you don't have to be perfect to win out.
Selective application of the 21:36/12 photperiod for only 1 or 2 weeks extends the wait only 2 to 4 Earth days, which makes up the missing 2 complete day and night cycles each week on Planet Ito. This permits the additional light energy to be provided without purchasing additional equipment or overloading existing circuits, which maximizes the existing system's capabilities. The main advantage is that matched with co2 and optimal nutrition, the plants metabolism will increase dramatically. I have only successfully tested this photoperiod for two weeks. The potential for a net increase of 40% over the entire cycle (80% increase in light energy vs. 40% longer wait) is worthwhile. Don't be afraid!
Day 1 - Sunday, 6:00am til Monday, 3:36am
Day 2 - Monday, 3:36pm til Tuesday, 1:12pm
Day 3 - Wednesday, 1:12am til Wednesday, 10:48pm
Day 4 - Thursday, 10:48am til Friday 8:24am
Day 5 - Friday, 8:24pm til Saturday 6:00pm