Ive got a Malawi girl that's nearly 20 weeks in flower, still got many pistils sticking straight up and no amber trichs. Im getting very antsy to chop.
Mine went quite a bit longer than that, but it was worth it. In a few more weeks start scoping all of the buds, mine started ripening one by one so I harvested that way. Usually I chop and hang the entire plant, but a lot of the long flowering landraces mature over a long period of time. Whatever you do, resist the urge to chop it early!