
Most MCU devotees, and even a wide swath of the general audience, know that July's The Fantastic Four: First Steps takes place in an alternate 1960s. Some of those people might even be aware that the movie's plot spans multiple years within that decade. But what most probably don't realize is that the film's big story beats connect to specific Fantastic Four Marvel Comics issues in an unusual fashion.
As presented by film YouTuber A Bit of Everything, The Fantastic Four: First Steps fit many of its major set pieces into a chronology that directly parallels installments from the original run on Fantastic Four comic books by the legendary Stan Lee and Jack Kirby.

For instance, the venerable First Family's first battle after getting their powers was with a subterranean creature called Giganto. That issue hit comic racks on August 8, 1961. In a scene from First Steps' trailers, the heroes stand on a plaque embedded in a Manhattan street. It reads:
"On this place, on this day, the 4 saved the city. A grateful city honors The 4"
The plaque is also embossed with artwork of the Fantastic Four (FF) fighting Giganto and a date for the dust-up: "On the Eighth Day of August."

Now, that could have been any old August 8. However, consider that much of First Steps' marketing has shown the team on a live Ed Sullivan Show-type TV program.
The implication of this sequence is that Reed, Sue, Ben, and Johnny decided to step even further into the limelight. This becomes more apparent with viral marketing from the film's official Instagram account. The in-universe video's voiceover promises a "closer look" at the Four:
"For nearly four years, the Fantastic Four have protected us. And now the Future Foundation invites you to get a closer look at the human beings behind the icons as we open the doors to the Baxter Building."

Movie clips have shown Reed and Sue conducting a guided press tour of the Baxter Building. Add all of these pieces together, and it becomes clear that the Fantastic Four have allowed the news media into their lives and homes on the fourth anniversary of the fateful spaceflight that gave them their superpowers.
No specific years are given in any of these materials, but if the Fantastic Four became who they are four years prior to this media push, it can be assumed that the clash with Giganto occurred on August 8, 1961.

Not only was the comic book issue with Giganto published on that exact day, but the book was the first-ever appearance of the Fantastic Four anywhere in our history. Ergo, the same likely goes for the MCU.
But this is not the only example of comic-movie synergy in First Steps. According to other observations from A Bit of Everything's video breakdown, the Silver Surfer arrived on Earth on Halloween night of 1966, as she warned citizens that Galactus was on his way.
This is evidenced by moments from the movie. When Shalla-Bal appears in the sky above Times Square, a group of kids in Thing costumes look upward in disbelief. In several bits of footage, sidewalks are also adorned with Jack-o'-Lanterns.

Moreover, Sue Storm is extremely pregnant as the Surfer hovers over her. Since she was not with child in mid-1965, Johnny and Ben put it together that she missed her period in early 1966. This would account for the late-stage size of Sue's baby bump when Galactus' Herald rolls up to New York on Halloween. October 31, minus nine months, equals the last day of January.
Back to the comics, the Silver Surfer (Norrin Radd in the comics' continuity) originally caught a cosmic wave to Earth in March 1966's Fantastic Four #48, only seven months before Shalla-Bal shows up in the movie's timeline. The issue also contained the first comic appearance of Galactus, Fantastic Four: First Step's main villain.
It's important to note that while Fantastic Four #48 was actually released in 1965, its cover date read March 1966. Cover dates are a gimmick used by the print industry to convince consumers that a given issue is still current. And indeed, Marvel.com gives issue #46's publication date as March '66, making it the commonly accepted release date as far as the public is concerned.
The concept of Marvel Time is also worth mentioning. Marvel Time is the publishing arm's nickname for the comic book universe's sliding timescale. It was implemented around 1968.
The intent of the sliding time scale is to allow comics to make contemporarily topical references to pop culture and current events, whilst keeping all the heroes ageless, no matter what year it is in the real world. Stan Lee put it best in a 1996 edition of the "Bullpen Bulletin" (via tedagame.com):

In short, it's Marvel's special trick from keeping the Punisher from being a 70-year-old man who's strapping a skull emblem to his chest and viciously disemboweling criminals (which, to be clear, would not stop Frank Castle).
Notably, though, the first seven years of the FF's comic book adventures were essentially told in real time since Marvel Time hadn't been invented yet.
As for how all of this relates to The Fantastic Four: First Steps, the movie's timeline adheres to the debut dates of certain comic issues, as well as the idea of Marvel Time, adds another layer to the movie's authenticity and cool factor.
The franchise hopeful The Fantastic Four: First Steps, from Marvel Studios and director Matt Shakman, hits theaters on Friday, July 25. It stars Pedro Pascal, Vanessa Kirby, Ebon Moss-Bachrach, and Joseph Quinn as Reed Richards, Sue Storm, Ben Grimm, and Johnny Storm, respectively. Julia Garner, Ralph Ineson, Natasha Lyonne, and Paul Walter Hauser make up the supporting cast. Matthew Wood supplies the voice of HERBIE.
A special thanks to A Bit of Everything for his in-depth research and timeline explanations from his video.
Could the MCU’s Fantastic Four Movie Match up To Marvel Comics in Other Spots?
Since Marvel Studios always keeps its cards so close to the vest, it's unknown if more comic issues will align with the Fantastic Four's sequence of events. The studio hasn't even clarified the finer points of the movie's narrative.
The only way fans can truly find anything out for sure is to be in the cinema during the last week of July when The Fantastic Four: First Steps stretches, clobbers, fireballs, and visually materializes its way into the eyes and hearts of the masses.
The MCU is also known for consistently taking creative liberties when adapting its source material. So, First Steps' already-discovered comic match-ups could be its only implementations of this element. But, to lovingly draw inspiration from Stan "The Man" Lee's distinct style for public declarations, there's still a lot of fun to be had:
"Worry not, True Believers! The Fantastic Four are here, and their show-stopping trials and tribulations are sure to excite in the trademark mighty Marvel manner!"