Boy they look like they are getting close but not quite there yet. The fall pullets do seem to take a little longer... I will guess you get your first egg on October 3rd.
Sorry for the confusion. meant red sex links, the ones I have had (usually the ones they call Red Stars, Golden Comets etc) are generally smaller than the black sex links. It has been my experience that the red sex links will lay a little sooner than the black sex links, on average.
It is hard waiting for that first egg isn't it, it does sound like some of yours aren't that far off. Hens mature at different rates, and 20 weeks is not that far along. Some of your girls are slower maturing breeds and will take a little longer than average. The black sex links are mixes...