Leaves droop and rise during lights out as well, so I'm not so sure that drooping leaves is a sign of too much DLI.
I 100% disagree with that Azi. I have seen tent growers back their lights off 2 hours and send certain varieties into flower from 18/6 to 16/8. I've also seen too many folks move plants outside from 18/6 to whatever they're getting in late spring (14/10?) and send their plants into flower.
Plants don't need 12/12 to flower or no plants would start to flower outside until late September. They need a shortening of their light period, which tells them winter is on the way.
@Jon shorten your hours at your own risk. I would recommend leaving them right where they are, droop be damned.
Not me.
They're being pretty wishy washy with their recommendations. If that's they're approach they should say for expert growers only. Since you're sticking by their chart you will end up seeing what a new grower would experience.