Martagon section lilies (Ll. martagon, hansonii, distichum, medeoloides, tsingtauense) can grow significantly during the growing season without a stem above ground, but I don't know about other lily types. Perhaps others will know. This holds true for all their hybrids. Although it is certainly acceptable to transplant martagon section bulbs in the fall, experts say transplanting in early summer, soon after blooming yields better results. So this optimal time would be about 1½ to 2½ months after your normal last frost date.