The Collaborative International Dictionary of English v.0.48:
Lateness \Late"ness\, n. The state, condition, or quality, of being late; as, the lateness of his arrival; the lateness of the hour; the lateness of the season. [1913 Webster]WordNet (r) 3.0 (2006):
lateness n 1: quality of coming late or later in time [ant: earliness]