Potency has two parts, really. First is the average maturity of trichomes on the plant (this is commonly reduced to percent amber). This is your global-level potency calculation. Clear trichome heads will have no psychoactive effects. Cloudy trichomes are indicative of cannabinoids having been formed in the trichome head. Amber trichomes are indicative of cannabinoids having been formed in the trichome head and have oxidized/degraded into less psychoactive cannabinoids. Second, your potency will change throughout your day/night cycle. This is your local-level potency and matters little.
The old amber rules are completely nonsensical. Most cultivars deposit trichomes in waves, and have trichomes mature from clear to white in waves, and have white turn amber in waves (not necessarily in that order every time). As long as the plant isn't throwing down new trichomes to have turn cloudy, you might as well harvest. You can always degrade your goodies later, but without chemical assistance you cannot un-ruin your ambers back to milky...
If you are growing for washing or sifting or concentrates in general that rule goes even further out of the water. Different trichome colors are different head sizes and impact hashish quality and mass. I know folks that are real hash heads that don't do a single thing related to the industry anymore except grow good washers above 5%, make hash rosin, and do isomer shifts on the rosin for a new-level stone. These people regularly harvest at 7 or 8 weeks flower to zero detriment. I can get behidn this more than cultivators growing exclusively popcorn nugs only for med/rec programs just because their room gets one more popcorn boof cycle per year.