The Collaborative International Dictionary of English v.0.48:
Nightlong \Night"long`\ (?; 115), a. Lasting all night. [1913 Webster]WordNet (r) 3.0 (2006):
nightlong adj 1: lasting, open, or operating through the whole night; "a nightlong vigil"; "an all-night drugstore"; "an overnight trip" [syn: nightlong, all-night, overnight]