The name of the device, the Atavachron, is quite a descriptive one. "Atavus" is Latin for "... (an) ancestor or ancestral type from which a character is assumed to be inherited", and "chron" is Latin for time, so, in essence, an Atavachron is a device which can send you to an ancestral place, of any time period.
The title is taken from "Macbeth" by William Shakespeare, Act 5, Scene 5: The title character speaks "Tomorrow, and tomorrow, and tomorrow, / Creeps in this petty pace from day to day / To the last syllable of recorded time, / And all our yesterdays have lighted fools / The way to dusty death."
According to the stardate this episode is chronologically the last of the series, even though its production number and air date are earlier than Star Trek: Turnabout Intruder (1969). This is therefore the last voyage of the USS Enterprise in the original series. This is also the last time travel episode of the original series.
Mariette Hartley (Zarabeth) was not allowed to show her belly-button in this episode, despite the appearances of other women's navels in previous episodes. To comment on this censorship, Gene Roddenberry gave Hartley's character two navels in his pilot Genesis II (1973), stating that "the network owed me one."
The same wallpaper-like patterned artwork that was defiled in Star Trek: The Cloud Minders (1969) appears here on a smaller canvas hanging in the library behind Kirk when he twists Mr. Atoz's arm to find Spock and McCoy.
The planet is called Sarpeidon. This is an alternate spelling for the name of "Sarpedon", the name of four different characters from Greek mythology. The first Sarpedon was a son of Zeus and Europa, and brother to the kings Minos and Rhadamanthys. He reportedly became the founding monarch of Lycia, in Asia Minor (Anatolia). The second Sarpedon was a son of Zeus and Laodamia, and a king of Lycia in his own right. He fought in the Trojan War, and was killed in combat by Patroclus. The third Sarpedon was a son of Zeus and Lardane, and a brother of Argus/Argos. The fourth Sarpedon was a son of Poseidon, and prince of a Thracian kingdom. He was killed in combat by his first cousin Heracles (Hercules).
At 72 years old, actor Ian Wolfe was almost twice William Shatner's age of 38, yet still acquitted himself remarkably well in their on-screen wrestling match, with Mr. Atoz trying to force Kirk through the time portal.