Having said that, one of my favorite things to grow photoperiod seed from 12/12. I often find equal speed of maturation, with greater yield and quality in growing photoperiods of great genetics from seed under 12/12, compared to autoflowers of dubious origin grown at 24 or 20 hours of light.
I do observe that 24 hours of light produces larger plants, which seem by many nuanced detail to have had a “rough life”. They look inferior in health to plants I have seen grown at 20 hours of light, with a modest 4 hour reprieve from photon bombardment.
Of course, there are some exceptional (and always improving) autoflowering genetics these days, and the quality and harvest of an autoflower grown seed to harvest under long daylight hours is well evidenced.
From a perspective of, “What’s the best smoke I can harvest” there is great difference between the quality of photoperiod and autoflower genetics, on the whole.
From a perspective of, “What’s the quickest smoke I can harvest” there is little difference between the speed of a photoperiod grown under a flowering cycle, and an autoflower grown under a prolonged light period.
From a perspective of, “What’s the most smoke I can harvest (within a given time frame)” there is a contextual consideration; where in lower light intensities with limited CO2 concentration, one advantage afforded to autoflowers, is that they can slowly accrue a greater total energy store in each 24hour cycle, and thus synthesize greater biomass than comparative photoperiod genetics grown in the same time frame. Under higher light intensity with supplemented CO2, it may be that the approximate DLI of 60+ which is estimated for Cannabis can be reached, and that the twelve hours of darkness may be greatly beneficial to soil ecology and plant hormonal regulation; a higher quality of herb is harvested at still peak quality; whereas a side comparison of an autoflower provided identical light intensity and CO2 may experience diminishing returns on yield, and the plant morphology becomes bulked in growth from stressed metabolic systems, and thus provides a marginally bigger yield at potentially a disproportiately lower quality.
That’s to say that if you’re trying to make your real-life time in X months convert to the highest profitability potential from the greatest investment of inputs, the allure of day-neutral cannabis which can sponge light indefinitely due to its genetic ability to build ethylene and other flowering hormones without a dark rest period may not be as lucrative as originally imagined; it may be rather lower quality weed, and only slightly more in yield than a photoperiod genetic which is limited to its short 12-hour window of photon access; but which you have pushed through environmental control for the reduction of limiting growth factors.
Too there are breeders such as DJ short who recommend starting seed under an 11/13 photoperiod, to coax unusual expressions; particularly toward influence of narrow-leaf drug traits.
One theory these changes in expression are seen from such a marginal shift in light hours (12/12 compared to 11/13) is because of “DLI” or a plant’s photon apetite; belief that the 12th hour represents roughly 8.3% of the seedling’s total light apetite, and so therefore its internodal spacing elongates as it continues to grow approximately 8.3% greater in height each day than its 12-hour filial counterparts.
Another theory uses the logic of the equator at its crux: that the cultivation year in many equatorial climates is clearly delineated by two roughly six-month seasons: a Dry season and a Wet season. It is this 6-month period of time which corresponds to sunlight hours, where there are nearer to 13 hour day lengths in the dry season and nearer to 11 hour day lengths in the wet season. And so the second theory posits that starting seed under 11/13 mimics seed which germinates and emerges in the wet season; adapts to its current season, and anticipates the form it must become to successfully flower in the coming dry season. Conversely, the seed started under 13/11 mimics seed which germinates and emerges in the dry season, adapts itself appropriately, and prepares for flowering in a coming wet season. This miraculous trick is quite simplified in explanation through evolutionary adaptation; for it is logical that all seeds which germinate and emerge under an equatorial 11/13 season and reproduce are the ones which successfully flowered in the 13/11 season. And so, it is thought that our ancestral cannabis genetics from equatorial regions adapt readily to the diametrically opposed seasons they routinely endure, and that this mechanism of adaptation may be leveraged through the simple means of plus or minus an hour with a mechanical timer.
Nature evolves for aeons, waiting for us to hack it. Unfortunately, we most oft exploit it.
-Dr. Zinko