Early one Sunday morning, Squidward goes to his open window prepared to play his clarinet. Unfortunately for him, SpongeBob’s alarm goes off at that precise moment, causing his clarinet to be jammed deep in his throat. SpongeBob awakes and asks Squidward if he’d like to go jellyfishing, taking Squidward’s squeals of protest as a "yes." After finally dislodging the clarinet, Squidward answers the knocking of his door to find SpongeBob and Patrick waiting for him. When he refuses to come out, they believe it’s only to prepare for jellyfishing and repeatedly ask him if he’s ready.
At his wit’s end, Squidward asks SpongeBob why he’s not at work, to which SpongeBob sadly replies that the Krusty Krab is closed on Sundays. Hitting upon an idea, Squidward tells them to wait for him, closes the door, then sneaks out the back and heads for the Krusty Krab. It is indeed deserted, but as Squidward takes in a breath to play, SpongeBob and Patrick arrive calling for him. Squidward runs to the kitchen and hides in the storage freezer. When SpongeBob and Patrick can’t find him, they assume he’s already gone to Jellyfish Fields and leave. Squidward makes to exit the freezer but finds that the door won’t open. He feels slightly concerned, but also confident that someone will notice him missing and find him soon enough.
2000 years later, Squidward remains in the freezer, frozen solid. The door’s rusted hinges give way and Squidward falls to the floor. Someone resembling SpongeBob with jet boosters hovers by and sees the frozen cephalopod, takes out a hammer, and proceeds to use the hammer’s laser function to thaw Squidward out. Dazed and slightly burnt, Squidward asks if his rescuer is SpongeBob, who answers that he is actually SpongeTron. Squidward discovers that he is in the future, where the world is covered in chrome and SpongeTron is but one of 486 clones. Horrified at this prospect, Squidward begs for a way to get back to his own time. SpongeTron directs him to a time machine conveniently located next to a room-sized can opener. Squidward decides that if he can’t escape SpongeBob’s descendants, he’ll travel to a time before SpongeBob was born.
The time machine arrives in the primordial sea. Squidward walks among the ancient sea creatures, hopeful that he can finally play his clarinet in peace. However, a shadowy figure pursues him, soon revealing itself to be a Primitive Sponge. The Primitive Sponge tentatively examines Squidward, who tries to back away but is halted by the presence of a Primitive Star. The two remain curious about Squidward, but are soon distracted by a jellyfish, which they are visibly frightened of. Taking his chance to get away, Squidward tries to play once more but is constantly interrupted by the screams of the primitives, who are zapping themselves with the jellyfish in their hands. Squidward has them hand over their loincloths, of which they have plenty, and proceeds to fashion jellyfish nets for them. Amazed by Squidward’s demonstration of jellyfishing, the primitives take the nets in earnest.
With nothing left in his way, Squidward begins to play at last. However, the wailing of the clarinet drives the primitives mad with rage and they chase after Squidward. Barely making it back to the time machine, Squidward jams the lever up and down and breaks it, sending the machine hurtling through dimensions before arriving to a world of emptiness. Squidward is glad to have somewhere he can be alone, but the utter solitude proves too much for him to bear. After searching all across the void, he finally crashes into the time machine and bangs the controls, wishing for it to take him back, even if it’s to SpongeBob.
At his words, the time machine returns Squidward to his home with SpongeBob and Patrick awaiting him. Squidward quickly recounts his adventures and tells the two how much he's missed them. When they ask him if he’s finally ready for jellyfishing, however, Squidward soundly refuses and demands to know who invented such a foolish game in the first place. They happily remind him that it was, in fact, he who invented it, and Squidward deeply considers going back.
The German name for this episode is "Die Zeit-Maschine" (The Time Machine).
This is the only time the title card letters are floating.
The episode, which arises from Squidward time-traveling and inventing the game of jellyfishing while seeking to avoid SpongeBob and Patrick as they want him to jellyfish with them, is a time paradox known as a causality loop.
Thus, a person is inspired or driven by an event to time travel and, whether or not intentionally, causes the event which will facilitate their initial time traveling trip.
The background of this episode's title card is also seen in "Can You Spare a Dime?" when Squidward pictures himself as an astronaut.
Either Jellyfish Fields was never made chrome, or the chrome coating fell away within the following 1000 years.
This is the first time Squidward swallows his clarinet. The second was in "Squidtastic Voyage."
The special "SpongeBob B.C. (Before Comedy)" seems to take place after the prehistoric time period shown in this episode, as the primitive characters in that episode are more civilized and have developed a simple language.
Three scenes of this episode can even be seen during the special's original song "When Worlds Collide."
When Squidward is in Nowhere, his footsteps make different sounds than usual.
SpongeTron mentions that he has 486 clones, one for each letter of the alphabet.
This means over the course of the two millennia, 460 more letters have been added to the alphabet.
In the future, the entirety of Bikini Bottom is covered in chrome, except for the hinges on the freezer door, which had been rusted over the last two millennia, the freezer's interior, the time machine's interior, and the Bikini Bottom civilians.
When Squidward says, "What are you simpletons doing?!" Primitive Sponge makes a surprised face that has become a popular meme on the internet and Twitter.
The jellyfish seen in the past was comparatively smaller than the present day's jellyfish.
This is one of the few episodes in which the Krusty Krab is featured without Mr. Krabs.
This is justified, since it was a Sunday and the Krusty Krab isn't open on that day.
In the Polish dub, SpongeTron is called "SpongeBot" and Patron is called "PatrickBot."
This episode premiered on New Year's Eve of 1999 along with several other Nicktoons episodes with futuristic themes in celebration of the new millennium.
This episode is the third of eleven episodes to be released on a Blu-Ray disc.
The Prehistoric part takes place sometime between 270,000 and 250,000 millennia ago because Trilobites existed 521,000-250,000 millennia ago, Ammonites existed 400,000-66,000 millennia ago, Sponges started to exist sometime between 635,000 and 541,000 millennia ago, Starfish started to exist sometime between 541,000 and 485,400 millennia ago, Jellyfish started to exist 505,000 millennia ago, and Flatworms (Tapeworms) started to exist 270,000 millennia ago.
This episode may take place after "Patrick! The Game" because, in this episode, Patrick knows people invent games, and in "Patrick! The Game" he thinks games grow on trees.
Even though the Krusty Krab is closed, the doors remain unlocked.
Throughout two millennia, Squidward's face can be clearly seen through the freezer window, where he should have been noticed by anyone working in the kitchen.
Additionally, the freezer would not have been utilized for its intended purpose: to store and retrieve food for use in the restaurant.
SpongeTron somehow knows Squidward's name, even though Squidward never tells him.
It's possible that SpongeTron, being from the future, is somehow able to tell what his name is using advanced technology.
It's also possible that SpongeBob told his kids about his "friend" Squidward, and the stories passed on through generations, and SpongeTron remembered them.
If the present day of the episode is assumed to be precisely 2000 years prior to the day Squidward wakes up in the future, March 6, 4017, that would make it March 6, 2017, which is a Monday, not a Sunday.
When Squidward exits the can opener room, there is a spot between his legs and his shirt that flickers from blue to brown for a few frames.
When Squidward enters the time machine in the future, there is one red and one green light above the door. When he next exits the time machine in the past, there are two red lights at the top.
The first time Squidward enters the time machine, the switch reads future on the top and past on the bottom. The next time he enters, the two are reversed.
When Squidward enters the time machine, the door knob changes sides.
When Squidward goes up to the bush where Primitive Sponge is, Squidward puts one arm towards it, but in the close-up he uses two arms.
Also, he would have needed to put his clarinet down. However, he does not put it down in the prior scene.
When Squidward runs in Nowhere, his clarinet disappears, but when he falls back into the time machine, it reappears. It then disappears when he exits the time machine.