I can see why you wouldn't want to take a chance starting you flush too early. I always take starts off my plants. Did you? The reason I ask is that even though you may have been told they are 8 week plants, sometimes things take longer. Does the possibility of the taste changing mean they'll be any less potent? I don't think so. Once you've grown this strain and get the timing down then you'll know for sure how long they take and the next batch you can flush at the right time. I'd watch them close and when you think you're a week or so out then start flushing them. Even if you do it for only 2 or 3 days it'll be better than not at all.