Looks like a nice plant, cheers. If you have amber trichomes at this stage I would bet money they are from the bud being touched and causing them to degrade early. As a general rule, you should ignore any suggested flowering times made by breeders. Their flower times mostly apply to their specific phenotypes and grow.
Determining maturity isn't about one single factor, its about watching ALL the signs the plant is giving you. As you grow more plants you will begin to be able to read those signs, and understand what point your plant is at.
FIRST the stigma(pistils) will turn red and begin to actually shrink/shrivel back towards the buds. THEN the bracts(calyxs) will begin to fatten up internally. The buds won't be appearing to grow much outwardly at this point but will be adding density and weight still. I've watched strong stems bend over in just a couple days during this period from the added mass.
FINALLY after about 2ish weeks of swelling, AFTER the stigma have turned, then you can look at trichomes on the actual buds and determine your final harvest point.
There are plenty of variables that can alter time periods, primarily genetics, and the growing environment. For the most part though cannabis plants follow pretty consistent patterns of growth and ripening.
It is VERY EASY to harvest a plant too early and loose out on flavor, smell, yield, and overall quality.
It is VERY HARD to over ripen a plant. I have never seen someone accidentally do it without ignoring plants for WEEKS. The best smoke comes from fully ripened healthy plants.