This is the species daylily "Hemerocallis Citrina," and quite possibly the variant "Citrina Vespertina." It is a nocturnal bloomer -- opens in the afternoon and blooms through the night. Also producing a fragrance, "Hemerocallis citrina" has 5-inch tight trumpet-like blooms. It is quite tall (over 4 foot high in my garden), and it is heavily branched. It blooms from mid June until late July.