1950 ("long ago")
- Fantastic Four (1961) #1, page 22.2 to 22.9 flashback: After being ridiculed for his ugliness, the Mole Man strikes out alone to find the land at the center of the Earth. After traveling the globe he washes up on Monster Isle, and enters a strange cavern. Mole Man finds the center of the Earth, but is blinded in a sudden avalanche. (The clothing being worn by characters in this flashback leads me to believe that this takes place somewhere in the post-World War 2 era. I have chosen 1950 on a whim.)
- Mole Man learns to sense things like a mole, and develops a radar sense. He masters the creatures below the earth, and uses them to carve out an underground empire. (Mentioned in Fantastic Four (1961) #1 page 23.1 and 23.2)
- Work begins on a memorial statue (that will be melted by a Skrull posing as the Human Torch in five years time). (Mentioned in Fantastic Four (1961) #2 page 3.2.)
- This is the latest year in which Reed Richards can begin constructing his rocket to the stars. (Mentioned in Fantastic Four (1961) #1 page 9.6)
Before Fantastic Four (1961) #1 origin flashback
- Reed Richards and Susan Storm are engaged to be married. (Mentioned in Fantastic Four (1961) #1 page 9.4.)
Tuesday 4th April, 1961
- Fantastic Four (1961) #1, page 9.1 to 13.8 flashback: Reed Richards, Ben Grimm, Susan Storm and Johnny Storm fly Reed's test rocket into outer space. They are bombarded by cosmic rays, and after landing the shuttle discover that they have all developed super-powers: Reed can stretch, Susan can turn invisible, Johnny can burst into living flame, and Ben has become a hulking monster. They decide to aid humanity, calling themselves the Fantastic Four. (The only requirement for placing this flashback was that it had to go before Yuri Gagarin became the first person in space on April 12th. I chose the 4th day of the 4th month for my own amusement.)
- Fantastic Four (1961) #2, page 6.8 flashback: Reed uses his stretchy arms to hail a passing plane.
July/Early August 1961 (before Fantastic Four (1961) #1)
- Atomic plants in Australia, South America and behind the Iron Curtain are dragged beneath the earth by an unknown force. (Mentioned in Fantastic Four (1961) #1 page 14.3 and 15.1)
Tuesday August 8th, 1961
- Fantastic Four (1961) #1, page 1.1 to 25.7: Reed Richards fires his signal flare to summon the Fantastic Four. Susan, Johnny and Ben all make their way across the city to Reed's apartment, where he tells them about the disappearing atomic bases. The FF track the cause of the disappearances to Monster Isle, and they confront the Mole Man and his monster hordes in his lair deep beneath the earth. The Mole Man's domain, and Monster Isle, are destroyed in an atomic explosion during the conflict, but the FF manage to fly to safety. (I have placed this story on August 8th, to match the release date of the comic.)
Between Fantastic Four (1961) #1's origin flashback and Fantastic Four (1961) #2
- The Fantastic Four establish a number of secret apartment hideouts. (Mentioned in Fantastic Four (1961) #2 page 11.1. This probably happens between FF #1 and #2, but it's possible that it was done before they fought the Mole Man as well.)
Before Tales to Astonish (1959) #27/1
- Henry Pym learns judo. (Mentioned in Tales to Astonish (1959) #27/1 page 6.6.)
- Tales to Astonish (1959) #27/1, page 2.6 to 2.7 flashback: At a monthly meeting of his scientific peers, Henry Pym is mocked for his outlandish ideas. (This flashback takes place several months before Tales to Astonish (1959) #27/1.)
Between Fantastic Four (1961) #1 and #2
- The Fantastic Four become well known public figures. (Mentioned in Fantastic Four (1961) #2 page 2.2.)
- The US military prepares special cells designed to imprison the Fantastic Four. (Mentioned in Fantastic Four (1961) #2 page 8.2.)
- The alien Skrulls, who are planning to invade Earth, learn of the Fantastic Four and decide to eliminate them. (Mentioned in Fantastic Four (1961) #2 page 16.5.)
Thursday September 28th, 1961
- Fantastic Four (1961) #2, page 1.1 to 3.6: Four Skrulls impersonate the Fantastic Four while committing acts of sabotage, theft and vandalism.
- An order is put out by the US military that the Fantastic Four are to be shot on sight. (Mentioned in Fantastic Four (1961) #2 page 4.1.)
Friday September 29th, 1961
- Fantastic Four (1961) #2, page 4.1 to 10.7: The real Fantastic Four are laying low at a hunting lodge, but the military manages to track them down and arrest them. The FF are placed in special holding cells, but all of them escape and fly away in a stolen helicopter.
- Fantastic Four (1961) #2, page 11.1 to 24.5: The FF track down and defeat the Skrull impostors. They then fly a shuttle to the Skrull mothership in Earth's orbit, masquerading as Skrulls themselves. Reed manages to trick the commander into believing that Earth's defenses are too strong to risk an invasion. The Skrull fleet retreats. The Skrull impostors, who are still captives on Earth, promise not to cause trouble as long as they are given lives where they can be contented.
Sunday October 1st, 1961
- Fantastic Four (1961) #2, page 24.6: The Fantastic Four leave the three Skrulls, who have been hypnotised into believing that they are cows, to graze in a pasture.
Friday October 27th, 1961
- Tales to Astonish (1959) #27/1, page 3.1 to 3.3 flashback: Henry Pym has nearly completed his newest invention, a serum that can shrink anything. He daydreams about its possible applications.
Saturday October 28th, 1961
- Tales to Astonish (1959) #27/1, page 2.1 to 7.8: Having completed his serum, Henry Pym tests it by shrinking a chair, then returning it to its normal size. He tests it on himself, but shrinks faster than he had expected. He runs outside in a panic and attracts the attention of a nest of ants. Pym runs inside the ants’ nest to hide, and is chased mercilessly by them. A friendly ant helps him to return to his home, where he uses the enlarging serum to return to normal size. Pym decides the serums are too dangerous, and pours them down the drain. (I have moved this story forward a month from its publication date so that it doesn't fall on the same day as Fantastic Four (1961) #2.)
- Tales to Astonish (1959) #27/1, page 7.9 to 7.10: At a monthly meeting of his scientific peers, Henry Pym tells them that he has abandoned his crazy ideas. Even so, from now on he will never again knowingly step on an ant hill.
Between Fantastic Four (1961) #2 and #3
- The Fantastic Four purchase the tower of the skyscraper that serves as their headquarters. Reed Richards redesigns the roof so that it will work like the deck of an aircraft carrier. (Mentioned in Fantastic Four (1961) #3 page 5.6. Reed presumably designs the Fantasticar and other vehicles at this time as well.)
- The Invisible Girl designs costumes for the Fantastic Four. (Mentioned in Fantastic Four (1961) #3 page 7.1.)
Tuesday December 12th, 1961
- Fantastic Four (1961) #3, page 1.1 to 5.7: The Fantastic Four are in the crowd watching a stage magician called the Miracle Man. The Miracle Man shows off his seemingly limitless powers, and uses them to humiliate the Thing. The FF return to the Baxter Building, while the Miracle Man decides that the time has come for him to conquer the world.
Wednesday December 13th, 1961
- The police commissioner receives a note from the Miracle Man declaring his attention to conquer the human race. (Mentioned in Fantastic Four (1961) #3 page 8.8.)
- Fantastic Four (1961) #3, page 6.1 to 23.7: The Miracle Man uses his power of illusion to animate a giant monster statue in order to help him steal an experimental atomic tank. The Human Torch destroys the statue, while the Invisible Girl trails the Miracle Man to his junkyard hideout. The rest of the FF arrive, and the Human Torch creates a bright flash that blinds the Miracle Man and negates his powers. After the Thing complains that he's getting all the credit, Johnny quits the team in anger.