It's hard to tell for sure. One way to tell would be to put a small piece of tape on the stem of a few of those that are in full bloom, late in the afternoon. Then go out the next morning, and see if those ones are still blooming. Could also be that different colours or varieties may have different growth habits.
I had beautiful day lilies but this summer the heat and drought put a lot of stress on them. I had flowers for one week but they haven't bloomed since. Last year they bloomed continuously for about a month. I live in the Midwest, not sure if that makes a difference.