I divide only when blooming slows. Otherwise, I consider if "it ain't broke, don't fix it".

kay

Some seem perfectly happy in a big clump and others might sulk or the bloom size become smaller. It's rather individual. It's not vital to divide like it apparently is with iris. If you see one go downhill, divide it. Otherwise, leave them until they outgrow their spot.

Nancy

Some daylilies will stop blooming from the center of the clump. When that happens, I divide.

Debra