The Collaborative International Dictionary of English v.0.48:

Timeliness \Time"li*ness\ (t[imac]m"l[=e]*n[e^]s), n.
   The quality or state of being timely; seasonableness;
   opportuneness.
   [1913 Webster]

WordNet (r) 3.0 (2006):

timeliness
    n 1: being at the right time [syn: seasonableness,
         timeliness] [ant: unseasonableness, untimeliness]
    2: timely convenience [syn: opportuneness, patness,
       timeliness] [ant: inopportuneness, untimeliness]