Antonyms of soon:
reluctantly, forcibly, willy-nilly, involuntarily, unwillingly, laggardly, lingeringly, ploddingly, sluggishly, deliberately, leisurely, belatedly, delinquently, tardily, slow, slowly.
Examples of usage:
  1. More of this soon!
    "Correspondence of Wagner and Liszt, Volume 1", Francis Hueffer (translator).
  2. He will soon be here!"
    "In the Border Country", Josephine Daskam Bacon.
  3. She asked me to let him have them soon."
    "The Head Girl at the Gables", Angela Brazil.