Granted, it was the late 1930s, but that was still 30 years prior to the airing of episode. That's less than the time difference between now and Star Trek IV.

Time Travel can be great if done right. It's rarely, if ever, done right in every franchise so it becomes a trope and ultimately damages the franchise. I typically despise most Star Trek "time travel" episodes and movies. But City on the Edge of Forever is good sci fi.