I was really impressed that I didn't get (much) light bleaching. I got more stretch than I hoped for, and had the top of some buds about 10 inches from my TSW 2000. I re-hung things, and now it's 15" from the tallest, sites, but I absolutely cannot move the light up anymore - there's like 1.5 inches between the light and the top of the tent! Which is a long way to say that at 24", in flower, raising the light might not be needed.
3 weeks is a bit early to be seeing any nitrogen fade, so I'd consider nutrients/watering sched, while not wanting to make any big changes. Good luck.
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