You've got 2 weeks at the minimum personally if not more, I don't see any fox tailed parts of the bud in that pic. The pistils have not even began to recede into the calyxes and too many of the pistils are still white.
As far as the dark period is concerned the scientific backing on that is....
When the lights go out the water drops back down to the soil/medium and the unmoveable nutes/acids start working. Basically the 2 main reason for that is to not have so much water weight in the plant when you harvest, and quick maturing/finishing up the trichs (NOT creating more but maturing the existing ones). The first holds more truth to it than the latter though, I do the dark period to lose a little more water weight but as far as the trichs maturity I have not seen enough of a result to be confident in that.
Jeweler's loupe you can generally find at a jewelry, hobby, bead store or those type of stores. Other than that you're buying online, which isn't bad or anything.
You've got a few more weeks, more of the pistils are showing color in this pic than the last. You can definitely see the development between the two pics.
Hope this helps all.
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