Thanks man, good to know. So what is reason for 15 min recommendation? And, what is likelihood of measurable stretch 2 mins vs 15, after plant has gone thru stretch phase?
I don't know the 15 mins recommendation, from what I know 2000-4000μMol is recommend for EoD treatment. One need to know how much far-red his light puts out per second and figure out how much seconds it need to get there.
Such puks have 14-15μMol/s PPF.
First you convert this to your own area (with a 4x 4' or 1,44m² area it would be ~ 10μmol / s / m²(15μMol : 1,44m² = 10,4μMol/s/m²) and then you can multiply it until you have reached the desired value. 200sec for 2000μmol, 300 for 3000 or 400sec for 4000μmol.
With a smaller tent it takes less time.
A 2x 2' only has 0,36m², 15μMol divided by 0,36m² = ~40μMol/s/m² and it needs only 50-100seconds to get the desired 2000-4000μMol.
And when the stretch is done there is no additional stretch when using far-red. Maybe the flowers are not that dense when its too much far-red (like with hps) but I don't think so.
From what I have seen one get only significant more stretch when use it either from the beginning or when they get too much from far-red EoD treatment.