I’m in SC.
Check with your local nursery.
Depending on their growth, your daylily clump will usually become crowded after four to five years and flowering will diminish. In most areas, late summer is the best time to divide daylilies.
I have done this activity in the early and late spring with great results.
Late summer, after they finish blooming. Don't be shy when dividing your day lilies. I use my garden spade and hack away. Plant the divided roots as soon as possible.