A good question. I don't know. But I suspect there might be differences between the different cultivars out there. Isn't there a yellow berried one (or two), too? I don't know what is normal, but I've seen wild ones a few miles south of the Canadian border in Minnesota at Thanksgiving time and they have their full berry complement, still. Wondering if Cedar waxwings will have migrated already before the color change.
Remember you'll want to get compatible males and females. Some don't bloom at the same time for good pollination.