The main problem with pumpkins is that they have a quite thin rind so the longer you leave them sitting on wet soil the greater the risk of rot from below. What appears to be a smashing specimen is anything but once cut from the plant. I'm not saying yours are but this is what I have seen.
So if they are simply for decoration cut them early as long as they are fully coloured, say mid to late September then store until needed. If they are not fully coloured wait until they are.
My hoochie coochie kuri also known as Uchiki Kuri are almost ready. The vines are already dying back. They are ninety day planting to harvesting so pretty early. However leaving them to ripen further results in denser flesh and longer keeping. I often pick off one at a time leaving the rest to harvest in mid October along with all the other squash I grow.