Hey, to answer your question, the indications marked on the packaging are just an approximate guideline. Each plant has its own genetics. It's like kids; they won't all be the same and won't die at the same time. You can harvest two identical plants planted at the same time and harvest them 3 weeks apart.
And the best is a pocket microscope, depending on the effect you're looking for.
More white trichomes give a more cerebral, euphoric effect, while more brown trichomes give a heavier, more physical effect.
I hope I could help you! Have a great day!