That's a nice jungle there! I was wondering about your light dep, you are tarping at 8pm and taking it off at 8am is that right? Are you going to adjust the schedule once the sun starts setting earlier? Have you tried covering the plants earlier say around 6pm, and taking the tarp off anytime during the night?
For future adventures in light-spoofage I'm planning on building a permanent cold frame greenhouse with a supplemental lighting system as well as a black-out system so that I will always be able to fudge a little in whatever direction is needed while using as much natural sunlight as is available.