I would expect that the flowering time of daylily cultivars is very complex.
As perennials and since they neither require a cold treatment to flower (vernalization) nor a specific day or night length to flower I would expect that seedlings would flower as soon as they have reached mature/adult size, whenever in the year that occurs (as long as they have enough time to flower before winter arrives, in those locations which have severe cold winters, etc.)
Second, hybridizers in warm winter climate locations (Florida & California) have indicated that nearly all daylilies can rebloom. I agree with that as I have looked at the recorded information on reblooming in the daylily species and their early hybrids and have concluded that it is likely that nearly all daylily species can rebloom given the appropriate growing conditions. So that should mean that once a seedling has reached mature/adult size and flowered it should flower again on a definite schedule since each flowering episode will only be controlled by the amount of growth required by each new fan to produce a scape. Recall that every new scape is produced by a new fan. However, a seedling begins as a tiny plant and must grow to adult size. That requires a certain amount of time and growth tends to depend on the size of the plant already achieved. Once a plant/crown has reached adult size it should take the new fan less time for it to reach flowering size again as it does not need to start at seedling size. There is already a crown with a certain amount of stored resources that can be used to start growth until the new fan leaves produce enough resources to support themselves completely. So it should take longer for a seedling to reach its mature size and bloom for the very first time versus how long it should take for it to reach its second bloom period. All bloom periods from the second on should require more or less the same time or growth (at the same temperature and under more or less the same growing conditions).
However, locations with cold winter climates during which no growth can occur will cause changes to the simple growth and flowering pattern. The arrival of cold weather could simply stop development and that development could continue from where it left off the next spring. On the other hand cold weather could kill scapes and then the plant would have to restart from scratch the next spring. It might also be that cold weather effects might depend on how old or large a scape is when the cold arrives.
How long it takes a fan to reach flowering/adult/mature size will always depend on the temperatures it experiences - warmer means quicker (except above optimum temperatures).
