Harvest times are very controversial as everyone has opinions and different tastes, but I like to try to harvest right before 50% amber, maybe 40%, although everything is guesstimated through 35x magnification. My reasoning is, amber trichs degrade over time, and even though they are most potent right before degradation, I still try to have as many non-degraded trichs as possible, even if that means 30% are immature.
I also harvest to main colas, meaning no sugar leaves/popcorn nugs are taken into account. This usually means 8 week indicas and 10 week sativas, sometimes longer on the sativas as personal preference.