Thank you for your responses, all. Interesting points,
@Ezzjaybruh, about more stretch going from 20 to 12 compared to 18 to 12 light hours. I think I will do 18/6. By the way, is 16/8 safe for veg? I heard 18 is the minimum to make sure it doesn't flower or go herm.
I've adjusted my two lights to be at 50% power so it is 327 PPFD at seedling height, which at 18/6 light schedule is 21.2 DLI. I really want to drive the light with these plants for yield and quality.