great work mate , they must be close to harvest now if they ain't drinking as much.
I'd be tempted to harvest your weed at 2 different times so you can feel for yourself difference of harvest times. be careful going for too much amber trichomes, amber is sign of oxidization so you are going to transformed THC to something else(cbn i believe), you'll degrade THC to get mild CBN stone.
***Don't get me wrong going longer harvest will change effect, but falling asleep smoking weed and couch lock are two different things. i believe it's CBD that give couch lock and OG Kush is a high THC plant with little CBD so your weakening THC to gain CBN to get fake couch lock effect. I'd argue you'd be better off growing an weed known for high CBD and couch lock effect than turning a high THC plants into a sleeping pill.
*** again mate just my thoughts with no real research done, best is to do it the way you want and be your own judge on harvest times.