Cannabis is classified as a 'short day' plant as it is concerned with its photoperiodism. There are: (short day) (long day) & (day neutral). Although we call them 'short day' plants it is somewhat of a misnomer. The day-light length has no effect on the flowering mechanisms of plants. We call them 'short day' plants, but they actually require a LONG NIGHT. The trigger for any and all plants that require a specific photoperiod is only the dark period. I have ran several trials on Cannabis to show this first hand. The typical axis point is 9-9.5 hours of dark, some cultivars (cv.) require more. the larger majority of cv. are well into a safe zone at 11 hours.
If you are having issues of stress by choosing to run 11/13, make sure you are dealing with exquisite specimens to even begin to delve into this matter.
Yes plants love the off time, during the dark period photosynthesis 2 takes place as well as dark respiration, this is also the time the roots actively bulk up.
I have had no problems in the past showing that day-light length plays no role. I ran multiple runs showing that as long as I stuck to 11 hours of dark I could on occasion even run the light for 24 hours and then turn them off for 11 hours
on 12, off 12, on 16, off 12, on 6, off 12.....see a trend here?
On a sepperate but similar topic: The best way to force reversion from flower back into a vegetative mode that I have found, as in lets say you took some cuttings late into flowering being triggered, is to give them about 6 days of very short night periods. for the first week of my cuttings I always throw in about 3 periods of dark lasting 4 hours each
So, lights on 4, off 4, on 4, off 4, on 4, off 4 (24 hours), this can always be modified if you need to work on them or add more cuttings BECAUSE the day-light length plays no role. You are essentially resetting the 'far-red' accumilation that occurs as the lights turn off.
An extended day-light length can indeed cause stress to some cv., a good majority of the cv. that have been bred in the past decade have many negative aspects they have inhereted from jump-breeding, back-breeding, and self-crossing. If this is something you wish to do, find a cv. that will work for your needs, if you have weak genetics.....kill the plant, I cull a large number of plants in my efforts for efficiency and uniformity in my systems (or give away, since botanists have soft hearts for plants)