I generally harvest the lot of them and some will be under ripe but there is no good way of picking just the ones that are ready. I just cut about 1/3 of a bine off starting at the bottom and after I've picked the flowers from that, cut the next 1/3 until I have the whole thing cut down.
First year you might be able to pick and choose, but my bines are too short at about 14 feet and so thick that I'm not about to stand on an extension ladder picking for hours.
It seems early. Are you sure they are ready? I'm not sure how soon you'd pick in that part of the country. Mine are usually just starting to have some flowers turning brown on the tips. Peel them back and look at the glands and see what color yellow they are. Flowers should start to feel papery, not green and cool.