here's another answer to your question in a picture blue......
Looking good despite the problems you've been having.
If you're in flower, it's 12-12...I think you know that, but with veg, it's 18-6. My temps are about the same and I haven't had problems. With the screen I'd let them grow, I kept pushing mine under for the first week or so and is barely above the screen now. I think I should of just let them go.
They can rot, I've had that happen a few times. Frustrating.