Clearly, although the definition may not be the best on the market, you are more than capable of guiding yourself with them. If you have doubts about whether or not to cut your plant, I can help you.
This is not an exact rule, and I don't like a certain type of "taboo" that exists about being guided only by a pre-established rule.
It really depends on the use you give to your cannabis. In its early stages, the % of THC is higher, as these are the first cannabinoids it creates to protect its progeny ("seeds") from the genetic damage of UV rays. If you consume cannabis for recreational purposes, wait until they turn an "opaque white" color and barely 10% starts to be amber.
If you consume cannabis for medicinal reasons, the most useful are CBD and CBN. The latter is the degradation of text{THC}_text{v}, which will require a more mature plant, especially one with the highest % of "amber" colored trichomes, but without letting it wilt. As a general rule, 50-60% amber and the other 50-40% white.
And if you are a connoisseur, as is my case, who seeks the balance between both effects, you have to take into account the genetics of your cannabis. By preference, I let Sativas reach 60% amber and 40% white, and Indicas 60% white and 40% amber, so it's not overly euphoric, but also not overly narcotic.
P.S.: The larger the trichomes in "microns," the higher the % of oils and terpenes they have. That's why the best extractions in terms of effect/flavor are found around 90 microns. Letting it mature correctly also increases the flavor.
I hope this helps you in this and future crops.