While the notion of time as a dimension or property of space (space-time) had not yet emerged, a literary tradition of time travel was already well established, going back almost 2,500 years. The earliest known depiction of a mechanism for voluntary time travel was the 1881 short story "The Clock That Went Backward" by Edward Page Mitchell.
The scenes where Jim and/or Artie shift through the time portal look eerily reminiscent of the dimensional shift scenes in The Alternative Factor (1967). Note that this episode aired three months prior to the Star Trek episode.
When talking with Capt. Scoffield at the club, West mentions "The Unpleasantness". That is a nickname for the American Civil War.
When Colonel Vautrain tells West and Gordon, "Union General Sherman is no match for our own Gray Fox," he is referring to Confederate General Robert E. Lee.