Opposite words for soon:
reluctantly, sluggishly, deliberately, lingeringly, slow, delinquently, laggardly, leisurely, unwillingly, involuntarily, belatedly, tardily, forcibly, willy-nilly, slowly, ploddingly.
Usage samples:
  1. Isn't it too soon?
    "Marcella", Mrs. Humphry Ward.
  2. The question was, how soon?
    "Literary Love-Letters and Other Stories", Robert Herrick.
  3. But she soon would be, she felt.
    "The Enchanted Castle", E. Nesbit.
  4. " We will soon know," replied the other.
    "The-Motor-Girls-on-a-Tour", Penrose, Margaret.