Woofie: I start mine in 16oz red cups till I plant them out in May. I wouldn't change size unless you plan to keep them potted versus putting them in the ground and you can do that in June. Depending on the number of seedlings, I've planted as many as 5 seedlings in a 3 gallon pot. Daylilies are fairly hardy based on the cross or registered one you have. I have alot of them here both registered and seedlings. This year I decided to keep the seed starting to a minimum and not try to do so many. I wanted to focus on other perennials.
My poor daylily babies are getting wind blown now as the winds are coming in from the north again. BUT, it will surely harden them off.
