some people watch for 50-75% of the hairs to change to that reddish brown while others watch for the glands to turn from a clear-milky-amber color and pick when a few turn to the amber...like 10% or so. it's an indiviual preference so you'll have to experiment on how you like your finished product. the seeds will also show when they're ripe by watching for the pods to split open slightly...you'll know it when you see it. if you're doing a seed crop on purpose let them go until you start seeing a few drop off...then you'll know the majority are ripe.
after picking the plant i let it hang for an hour or two then put the scissors on it...after a short rest after picking the leaves will be much more pliable and easier to work with. makes it a bit easier to get your pointed scissors down to where the leaf stem meets the branch.