Yes, Daylily plants are very forgiving and can be divided Spring through Fall. They can even be divided during bloom, without harm if you are careful.
First, dig underneath the plant and lift it. Divide the roots so that each part has fans (green leaves), a section of the crown, and its own set of roots. Trim the foliage to reduce excessive moisture loss. Leaves should be no longer than 3-4 inches. Replant each section into its own pot or area of the garden. Bonemeal into the hole is good idea as is transplant fertilizer. Within two weeks you should see new green foliage emerging from the center of each fan. Keep your new divisions well watered during the summer.