Have you seen a positive difference vs 12/12? I don't like starting with 13/11 from day 1 of flower. Tried that and had too much stretch. This time figured I would do 12/12 for first 2 weeks then 13/11 then back to 12/12 last 2 weeks..
well, i haven't done an exact side by side comparing 12/12 to 13/11... so all i can offer is anecdotal evidence...
with the last run, i flipped at 12/12 and went to 13/11 after 2 weeks. then ended up diminishing at the end to try to encourage them to wrap it up. in hindsight, i don't think i like rolling the clock back on them once they're in bloom. to their seasonal perception, it pushes them back from 3 to 4 weeks overnight, and i think that may have contributed to them taking so long to finish up in the end...
in the current run, i really wanted to flip at 13.5/10.5, but since there's so many different strains in the tent i went for the less experimental 13/11. similar to the last run, these girls showed discernible floral tips on day 8... same flip speed between all 8 current strains vs the 3 previous strains. to me, this hints that there is still room to push the day longer at flip, but that would be very strain dependant.
now, given the diversity of the plants that i'm using, and my familiarity with most of them, i'd say that there is less stretch overall with the pontoons vs without them, regardless of a 12 hour or 13 hour day at flip. but i personally don't like the rolling of the clock back on them once they are in bloom and growing more hormonally sensitive... so from now on i will only be flipping at 13+ hours on the day, since i still want to max out the day length for the plants while still getting a smooth transition. that way i can still diminish towards the end if i want, or not, but any adjustments to be made would only be those that told the plant that it is now later in the season. in fact, i think that in the end, there is the most to gain from finding out exactly where that floral "hair trigger" night length is, and using that information as the basis for a diminishing light routine; give the plant the exact seasonal lighting times that it would get outside...
as to your stretch in the first week, do you bring the lights down a bit for that first week? stretch in this case is mostly influenced, in my opinion, by the genetics of the plant (how much does it want to spread out for the buds that it genetically knows it wants to make if all goes right) vs. the normal environmental variables that traditionally influence stretching, particularly light intensity. pre-flip, when you lolipop and whatnot, also reduce the inferior budsites in the mid- and lower canopy and spread out the dominant tops to allow maximum direct light contact, and reinforce increase in direct lighting with bringing the light a little closer to increase the intensity. those forces, in my experience will potentially* act against the stretchy tendencies of a plant that wants to get too leggy in the transition. i have a theory that if you transition a plant with a night that is too long past her genetically-dictated critical night length, that THAT is a substantial stress for the plant to deal with. now, i work on the theory that plants have a 2 week response interval, metabolically speaking. so, if we flip the mami with a night that is, to the plants phytochrome system, supposed to be 2 weeks after it started to flip (on an outside interval), then she's potentially gonna be like "DAMN, yo... WTF was i doing these past 2 weeks?!? i'm all fucked up now... gotta catch up 2 weeks, and it's gonna take 2 weeks to start to do that, then it's gonna be 2 more weeks later... shit, gotta get 4 weeks of stretching done in 2 weeks...". at least that is the inner dialog that i could imagine going down in a plant, if it were able to do such stuff, and also if my theories are close to correct...
*my Cotton Candy Kush missed the memo...
but ya, bro... i the end i think i just gotta leave it with this song, that my pandora hit me with while i was typing that wall o' text... it's popped it on me a few times when i've been in the garden, and i've always found it apropos. or maybe it was the dabs fresh in mah head...