Antonyms of later:
early, antecedent, advance, advanced, premature, anterior, fore, foregoing, former, precedent, preceding, previous, prior.
Examples of usage:
  1. See you later, Ruth.
    "Gargoyles", Ben Hecht.
  2. Three weeks later Andrew sailed, and soon after he had done so Wannop called one afternoon at The Firs, where he was received by Mrs. Olcott in the garden.
    "For the Allinson Honor", Harold Bindloss.
  3. If you don't tell me, you'll be made to tell later.
    "The Red Symbol", John Ironside.