Synonyms for In the old days:

• a. & adv.

  •once (adjective, adverb)
  • more before.

• adv.

  •once (adverb)
  • before,
  • already,
  • heretofore,
  • earlier,
  • previously,
  • late,
  • back,
  • sometime,
  • erstwhile,
  • one,
  • old,
  • bygone,
  • away back,
  • quondam.

• Other synonyms:

  •
  • atavistic,
  • formerly.
  •
  • removed.

Antonyms for In the old days:

• adv.

  • once
    later, future, presently, currently.