Bang on dude.had to be said lolWhat your seeing is the plant going into its rest cycle, and awaking again. Lights after the droop is a waste of electricity imho.
Drop to 18/6 will probably be about right.
... the pre-lights-out droops are a fairly common response,.. I get this on some of my outdoor photo's too! Well before sunset, they "relax" the leaves' postures,..... As for coco, never even let it get even close to dry, coco is not true soil, and doesn't react like it does either,... should be moist at all times, and with 15-20% run-off every time you feed,.. it's odd CEC characteristics are why it's treated differently than soil, or even peat-based soilless,...