You are a lot better off using 24 hours of darkness, using 55-60 degree temps, and turning on a black light for ten to fifteen minutes every four hours or so. You are right about nute uptake during Lights on! And how much nutes are really available after a two week flush? The UV from the black lights will make the plant do the same thing, but by converting stored sugars to do it, instead of taking up nutes fresh. Doing this will also help ensure that you don't lose a bunch of THC and CBD's during the first couple days of drying. Make sure you water the day before you turn the light off, so it isn't too humid, and doesn't get moldy. My cousin turned his lights off right after her waterred, and came back two days later to a room full of bud rot. He got a total of 2 ounces of good smokable bud off of 20 plants,
. His power went out too though, so his fans were off.