Source : Webster's Revised Unabridged Dictionary (1913)

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.

Source : WordNet®

lateness
     n : quality of coming late or later in time [ant: {earliness}]