The best way to determine ripeness is by using a microscope. Milky trichomes are ripe…
If there's no microscope available: harvest a bud from the middle and dry it quickly on the heater. It won't taste good, terpenes are definitely gone… But you'll know if it's ripe. I only use this method when all other signs indicate it's time to harvest: no more thirst, sun leaves are turning colorful, pistils (the little hairs) are all brown…