While I may be a straight male, even if autistic, I like The Little Mermaid franchise (besides, I really wouldn't call it a "girl's movie" or "girls franchise" since it featured plenty of testosterone-based action anyways). So, I decided to form a timeline on that series. Keep in mind that these are estimates based on stuff stated in various sources.
Keep in mind that the timeline will only cover stuff pre-Ariel's Beginning's release and won't cover Kingdom Hearts, obviously, especially since anything after Ariel's Beginning that specifically utilizes stuff from Ariel's Beginning is going to be excluded for reasons relating to continuity errors (Ariel's sisters were already implied to have a difference of one year each in the TV series and film, hence why I'm including the one year bit despite it being in Ariel's Beginning).
1.5 thousand years prior to the first film: Events of the forgotten history of Atlantica; Sharkanian Race and Merpeople fight each other; Atlantis destroyed; Centaurs flee to Olympus; Surfacing is banned, although Ariedne's descendants had at least one princess who desired to see the surface.
At least 100 years before the film: King Triton banished the Sorceress into her cave; Triton played his father's Neptune's Calliope, only for his playing to inadvertently wake up the Ancient Seaclops and destroy it.
22 years before the film: Aquata is born
21 years before the film: Andrina is born
20 years before the film (1816): The Sargasso War; Ursula is banished from Atlantica for creating dark tridents; Apollo is hailed as a hero despite his involvement being an accident; Arista is born
19 years before the film (1817): Atina is born
18 years before the film (1818): Adella is born
17 years before the film (1819): Alana is born
16 years before the film (1820): Ariel is born
15 years-1 year before the film (1821-1834): Athena dies.
1 year before the film (1834):
Ariel manages to conquer her fear of humans after witnessing Eric being kind to a dolphin (although as his back was towards her, she never got a good look), and proceeded to start her own collection.
Sometime later, Ariel managed to get captured by the Morays, with Aquata also getting captured when trying to save Ariel. Ariel managed to outwit the Serpentine, and
The Seaclops is forcibly reawakened as a result of Ariel's terrible playing of the Sea Calliope.
December 25, 1834: Ariel learns about Christmas from Spot and attempts to recreate the holiday for Atlantica; Urchin steals some items and food for his fellow orphans after a misunderstanding from Triton caused him to think Atlantica had no room for the orphans
Late December 1834-January 1835: Triton and Sebastian goes off for three tides to make a successful negotiation with the Olympian kingdom. During this time, Sir Figmond, getting irritated with the partying of the Flooglefish due to it depriving him of sleep, forms a petition and demands that the Flooglefish leave, eventually doing so without Dudley's consultation (as the latter was going too slow for them to wait), and despite his insistence that they do not do so. Floogleweed ends up quickly growing the next day, resulting in Atlantica being covered in it. Since Sir Figmond doesn't want the Flooglefish to return and the only other creatures who can eat Floogleweed are the Burpa Fish, the Atlanticans invite them to chomp down on the Floogleweed, despite both Ariel and Dudley's insistence on not doing so (the former opting that they apologize to the Flooglefish). Eventually, after they cause a ruckus after eliminating the Floogleweed due to their gluttonous nature, the Atlanticans demand that they be driven out, only to get Sharks instead as they are the only thing Burpa Fish fear, despite Dudley and Ariel's insistence not to. Ariel, after hearing Spot and his Orca pod's singing, lures the Sharks over to be chased off by the Orcas (as they are the only thing sharks fear). It was during this time that the Flooglefish are welcomed back just in time for King Triton's return. Triton then supplies his daughters with gifts from Olympia: with Ariel getting a necklace that she doesn't like. However, during her time playing with her friends, she accidentally lost it. The next day, due to a misunderstanding from Triton during dinner, the kingdom proceeded to try and find the necklace, which is then found by Sebastian and his nephews/niece during a hike. Shortly afterwards, the Seahorse tournament is announced. Ariel managed to secretly enter as a mystery rider against her father's wishes, and eventually stumbles on one of the players, Snapper, cheating. After Snapper in turns deduces that she was a mermaid (though not Ariel yet), Ariel decides to unveil her true identity, knowing full well she may have to face punishment for her actions, to expose Snapper's cheating. Ariel then managed to win the tournament and be the first mermaid to participate and win the tournament, although under the condition that she help Snapper clean up the stables. Sometime thereafter (presumably after Ariel managed to clean up the stables), the Blowfish tournament was to be done on the same day as Sebastian's birthday. Ariel then proceeded to go visit a sea monster named Caliban, who was spending his time moaning due to no one visiting him. Ariel then spent the next four days visiting Caliban, and after realizing they needed to prepare for Sebastian's surprise party due to his birthday being two days away, Ariel managed with her sisters and Urchin to prepare for the party (forsaking her visit to Caliban in the process, and also infuriating the chef as he had taken a full day to clean up the mess the Burpa fish left), resulting in Caliban coming to visit and also getting a spot on the Sea Lions team, managing to defeat the Atoll Octopuses in their first loss and Atlantica's first win, also reuniting him with his college friend Sebastian ("There Goes the Neighborhood"; Gone With The Waves; .
February 1835: Triton receives a request for his "cousin" Coralani to visit him. Unbeknownst to him, however, Pirania, a cannibalistic, a piranha-like sea-witch, learned of this development as well as Triton not remembering what Coralani looked like, and took to disguising herself as Coralani. A day later, "Coralani" arrives, with her abusive nature of the dolphins as well as her rudely telling Ariel off causing Ariel to become suspicious of her and try to warn her dad, though "Coralina's" lies managed to have Triton disbelieve her. Ariel then tried to have one of the orphans deliver a gift to "Coralani" as an apology for her earlier assumption to her, only for "Coralani" to nearly eat the orphan, resulting in Ariel smashing her on the head with the gift to save her, although "Coralani's" further lies had Triton not believe Ariel's claims further and causing even Ariel to wonder whether she was imagining things. Ariel then proceeded to try to apologize in person, only to see "Coralani's" true form, resulting in Flounder, Sebastian, and Ariel being petrified by her petrification spray, although Pirania frees Ariel and forces her to keep quiet with the subtle threat of having them remain petrified if she is to be exposed by Ariel, realizing that keeping her petrified would cause Triton to become suspicious of her. However, her Piranha-like nature proved to be uncontrollable and she ate up the table, causing even Triton to become suspicious of her, with the real Coralani arriving with her daughters. Ariel then accidentally petrified Pirania's body with her petrification spray, with Pirania's spell being undone on Flounder and Sebastian in the process. Pirania is then arrested by the merpolice and presumably freed from the spell after being securely locked up on Triton's orders.
Ariel initially gets beached for a third time after she managed to retrieve a human jug on the surface and implied to have surfaced in the process (especially due to Sharkanians being nearby at the time). She then tries to learn about Atlantica, and eventually learns the hidden history about Atlantica's foundation from Marlin the Wizard. Triton then managed to renounce the beaching afterwards.
Ariel managed to foil a heist on Pearl by Lobster Mobster and Da Shrimp, resulting in the latter quitting due to constant abuse as well as Lobster Mobster being placed in jail for a very long time, as well as retrieve the valuables he stole with the Abaloney Kid, although at the cost of missing her music lessons.
The events of the first movie (Spring 1836)
December 25, 1836: Ariel's first Christmas with Eric. Ariel organizes a scavenger hunt for Eric to find his gift, a ship in a bottle.
At least a year after the first film: Melody is born (1837); Morgana disrupts her presentation ceremony and holds Melody hostage in an attempt to force King Triton to give up his status as king, but Ariel narrowly manages to foil Morgana and force her to flee, although not before swearing revenge. Because of this, Ariel is forced to build a second wall around Eric's kingdom and hide Melody's heritage.
c. 1849: The main events of Return to the Sea.
This is all I can come up with at the moment. I decided to put the events of the movie at Spring due to the presence of blooming trees in some shots of Eric's kingdom, which bloom at the spring. As far as the year being 1836, that's because the events of the TV series, the Disney Comics, and Marvel Comics serials took place a year or two before the film, and Metal Fish most likely takes place AFTER the events of the Marvel Comics, and the events of Metal Fish strongly implied that the events of the film took place around 1836 (as Hans Christian Andersen decided to write the original tale based on his encounter, and presumably the bad ending was because he was a bit miffed at Ariel marrying Eric over him). I also had the opening of Return to the Sea take place a year after the film, in order to fit in some of the books (namely, Ariel and the Aquamarine Jewel, that book where Ariel managed to do a Christmas celebration, the Dolphin Adventure one). The other dates are based on what is stated in either the series or in the comics. The only book unaccounted for right now is Reflections of Arsulu, since I haven't read the book and there wasn't anything I could glean into that indicated anything about its setting, although I would have to assume that it was some time after the events of The Evil Manta due to Ariel getting suspicious of "Arsulu" after she pulled a similar trick to Evil Manta in his debut episode.
As far as some of the placements of the specific elements in the series, that's based on some key details in some of them (namely the comics. For example: The Marvel Comics had to take place between Save the Whale and A Little Evil, due to the fact that the Seaclops is still awake after the events of Calliope Dreams and Ariel managed to put him to sleep afterwards with singing, and clearly wanting revenge for being waken up earlier, Spot also makes his reappearance and she has him search out any intel on humanity (which meant it had to take place after Save the Whale since that's the only time in the series she encountered Spot AND was not afraid of humans, as she got over her fear and became fascinated by them in Thingamajigger, with her also expressing interest in human artifacts afterwards as a result of the same episode which is shown in the comics. In addition, Evil Manta's appearance in the first issue has him still being villainous, meaning it definitely was before A Little Evil, which redeemed him. On a related note, the events of Serpent-Teen had to take place between Thingamajigger and Against the Tide due to Ursula already having her lair by her debut, which she got from the Moray after Ariel's actions resulted in its death, and Ariel already collecting human artifacts strongly implies that it was after the events of Thingamajigger, since she started her (first) human collection after that episode.).
Anyone with suggestions on the specific placement of the entries (issues/episodes) for the TV series, Disney Comics, or Marvel Comics issues, or even any better suggestions for the placement of those things based on evidence from the TV series especially, or any additions especially in terms of books or comics (that AREN'T Ariel's Beginning or anything that alludes to the movie such as AB's birth order of Ariel's sisters, I must remind you), feel free to post them, as I'm glad to improve on this blog with any suggestions anyone has to offer.. For the record, don't post anything indicating that nothing except the original film is canon, because aside from the fact that they ARE canon, at least to the TLM franchise even if not to WDAS, that isn't the point, as this blog is supposed to be trying to create a timeline for the franchise.