Daffodils MUST produce new roots in the fall to live the next spring. If you were planting dry, bought bulbs, it would be too late to plant if you are in zone 4. But since these daffs are already in the ground, then you can transplant/divide anytime in October. Summer into early fall would have been better, because, unlike then, now you need to be very careful not to break the new roots off. If you break them all off, most likely no more will grow and the bulbs will die next season.
