These dates are those that apply to Maryland and were determined by Arisumi & Frazier. They found that the time at which the scapes start to develop is determined by when in the growing season the plants actually flower.
Early blooming cultivars initiate their scapes from July to October the year before they flower.
Early mid-season bloomer initiated scapes in December the year before they flower.
Late mid-season cultivars initiated scapes in March of the year that they flower.
In Florida, early, mid and late flowering cultivars had all developed scapes by February.
Those dates may well be misleading.
Daylilies develop their scapes when the growing point reaches some mature size. It is the last thing that a mature growing point does because it is destroyed (consumed) in producing the parts of the scape. The crown then must develop a new (replacement) growing point for the one that is consumed in producing the scape. That development starts, at the latest, when the previous growing point reached the size to stop producing leaves and to become the scape. The developing growing point may grow large enough to produce its own scape even as it develops and possibly even before it sprouts. That depends on the size of the crown, the fan of leaves and how well the daylily is being grown (how close to optimum conditions the fertilizer, light, water and temperature are).
In some plant species, the buds (growing points) with their inflorescences (scapes) can stack like nesting dolls. We do not know if daylilies can do that in locations where the growing season is very long and the winters are mild. I expect that they can do so. Most daylilies can rebloom and given appropriate conditions many can rebloom in even my location. That means that most mature daylily crowns are likely to have two scapes developed and stacked at some time.
In locations with long growing seasons and mild winters I would expect that if a daylily produces three scapes in a growing season then the time between the appearance of the second and third scapes is the amount of time that daylily requires to develop a scape (at the temperatures it experiences). Since temperature affects development time, the first scape to flower in a growing season will take longer to develop (due to lower temperatures during "winter" in mild winter, long growing season areas).
