When you harvest is a matter of preference really (what kinda buzz you want the cannabis to have) vs yeild loss from harvesting to early. More amber tric's will give more of a couchlock high , more Cloudy crystals will give the stone buzz type of high. Most indica dom strains take 7-8 weeks to fully flower (sativa dom strains can take longer)

From your pics your plant is in some trouble its leaves look very droopy and looks like maybe heat stress? But they should be able to make it another few weeks cannabis is a resiliant plant.