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]

Moby Thesaurus II by Grady Ward, 1.0:

28 Moby Thesaurus words for "timeliness":
   advantage, advantageousness, advisability, appropriateness,
   beneficialness, convenience, decency, desirability, expedience,
   expediency, feasibility, fitness, fittingness, fruitfulness,
   opportuneness, percentage, politicness, profit, profitability,
   propriety, prudence, rightness, seasonableness, seemliness,
   suitability, usefulness, wisdom, worthwhileness