Like all the other publishers, DC also published anthologies of weird stories (as opposed to continuing characters) in the 50s, but even before that, they had anthologies of adventure stories. The earliest time travel that I’ve found so far are from 1939: a two-part story of Slam Bradley and his sidekick traveling to the year two billion, A.D., in Detective Comics #23–24; and a five-part story, “A Playboy in King Arthur’s Court,” starting in in Adventure Comics #37. As for the 50s weird stories, the first one I found there was an [Error: Missing ':}' tag for wikilink]
History runs wild when Columbus, Napoléon, and Cleopatra journey through time from the past to the present!

Variants

(1)
  1. “DC Comics” by multiple writers and artists (1939).