Wall of text incoming:
Here are my findings on the junior novels of Black Panther and Thor: Ragnarok:
Black Panther:
First, this junior novel is unique in that it has a prologue. It is a scene that is not in the movie. It starts with a young T'Challa and Nakia in the catacombs, when they run into T'Chaka. At first I thought this was one of the deleted scenes you can find online, but this one takes place right before he goes to N'Jobu in Oakland. He tells the T'Challa and Nakia the catacombs are a place to pay respects to the ancestors and that they should play somewhere else. The scene shifts to present day where T'Challa lays his father to rest in the catacombs and is then called to the Royal Talon Fighter to get Nakia (where the movie starts).
The bonus story is called Black Panther: Aftermath, which takes place on the same day as the Siberia fight in Civil War. T'Challa takes Zemo to Everett Ross in Berlin. While Ross was interrogating Zemo, another agent was able to steal one of Zemo's belongings, a journal, in the evidence room. This agent is called Charmagne Sund, who turns out to also be Sokovian. Ross asks T'Challa to help him get back the journal. The two track down Sund to the Berlin State Opera. Just before they arrive they get shot, and one of the bullets goes through the Black Panther suit. Sund escapes, but T'Challa finds fragments of the bullets, which he realizes are Vibranium.
We get a chapter from Sund's perspective, which explains that she wants to kill Zemo, because he has ruined Sokovia's reputation. She stole the book in case he escapes, because she knows he would come for it, since it contains all his plans.
Back in the Joint Counter Terrorism facility, Everett Ross gets a call from Thunderbolt Ross, reprimanding him that he took Black Panther with him, without his approval. T'Challa mentions he's not an Avenger, but E. Ross says that doesn't matter to T. Ross. Meanwhile, T'Challa deduces that the Vibranium fragments are literally fragments from Ultron's vibranium supply in Sokovia. Then E. Ross is notified of explosions all along Unter den Linden.
Ross doesn't understand why Sund would plant explosions, while she could just escape with the journal. Then the power in the facility goes out, and T'Challa realizes the explosions and the theft were a diversion to lead the agents away from Zemo. Zemo is forced to the helipad by Sund, where she plans to shoot him. T'Challa reaches them and tries to talk her down, but she shoots him. Ross eventually catches up and shoots Sund in her hand. Zemo looks down the building, still wanting to end his life, but T'Challa gets to him before he can make the jump.
Eventually Zemo and Sund are arrested, and Ross thanks T'Challa. In the epilogue, T'Challa is flying home. He gets a call. It's Captain America. It's about the Winter Soldier.
Timeline placements:
Black Panther The Junior Novel - Prologue: April 16 2016, before Black Panther Chapter 1.
Black Panther: Aftermath - Prologue: April 10 2016, it's the scene with Zemo and T'Challa, so it's the same as
Captain America - Civil War Chapter 17: "Steve vs. Tony" (2:02:35 - 2:07:08)
Black Panther: Aftermath - Chapter 1: '''LATER THAT DAY. MUCH LATER'', so it should also be April 10 2016. This is before Ross enters the room to interrogate Zemo, so before
Captain America - Civil War Chapter 18: "We All Need Family" (2:12:14 - 2:12:58)
Black Panther: Aftermath - Chapter 2: ''TWENTY MINUTES LATER'', this is after the interrogation. So after
Captain America - Civil War Chapter 18: "We All Need Family" (2:12:14 - 2:12:58)
Black Panther: Aftermath - Chapter 3-13: These all take place within a couple of hours, I think at most 3-4 hours. Chapter 8 mentions the explosions began around three o'clock that afternoon. Siberia is ahead 5 hours of Berlin, does that work in regards to the placement of the Siberia scenes or does Aftermath need to move up a day? In Black Widow: Prelude, Thunderbolt Ross mentions that T'Challa has not responded to his inquiries. In Aftermath, Thunderbolt Ross does call Everett about Black Panther, so I think it's at least before
Black Widow: Prelude #1 (pg. 5-6). Probably also before
Spider-Man - Homecoming Chapter 2: "It All Begins" (0:07:34 - 0:07:48), then?
Black Panther: Aftermath - Epilogue: Flight back to Wakanda. In Infinity War: Prelude 1, Steve tells T'Challa he has some loose ends to tie up before they accept his offer. So this is after
Avengers - Infinity War: The Hero's Journey - Captain America (Chapters 1-9), since the story of Black Panther hasn't happened yet, but Steve does give T'Challa the call. We'll just have to assume that due to the events of Black Panther, Steve and Bucky are unable to enter Wakanda yet. It does however explain again why Shuri mentioned ''Another white boy to fix'', since now they know for sure Bucky is coming. So, April 14 2016, that gives Wakanda enough time to put T'Chaka in a casket and bring him to the catacombs on April 15, so T'Challa can pay respects on April 16. If you're wondering ''Why did T'Challa take 4 days to return after his business with Ross was done?'', well, Aftermath mentions multiple times T'Challa is afraid to go home now that T'Chaka is gone.
My consideration to put it on the timeline
Black Panther The Junior Novel - Prologue
Yes: Two new scenes (told in a frame story) that fit neatly in the timeline. No contradictions. Nice bridge from Aftermath to the opening of Black Panther. ''Adapted by Jim Mccann, written by Ryan Coogler''. The Thor Ragnarok junior novel had ''Adapted by Jim Mccann, based on screenplay by Eric Pearson''. So it seems like these new scenes were at least written by Coogler himself.
No: I'm not sure what the rules are with only placing a prologue on the timeline, instead of the full junior novel. However, this is the only junior novel to have one with new information, so it does have significance.
Black Panther: Aftermath
Yes: New story that adds some depth and information to the characters, written by Steve Behling who did the other canon novels. We already have the GotG Vol. 2 bonus story on the timeline, so this shouldn't be an exception. We know that one was canon, since it was referenced in another novel.
No: The story mentions Zemo was headed for The Raft. We know due to FatWS that Zemo did not end up at the raft at the end of Civil War.
However, he is never shown to be taken to the Raft in this story, it was only mentioned at the beginning. Perhaps the events of this story got Zemo a reduced sentence, because one of the governments own agents tried to and almost succeeded in killing him.
Besides, we have accepted other novels and comics on the timeline that have small contradictions that could be explained (Cosmic Quest 2 and GotG prelude, for example.)
Thor: Ragnarok:
It's called Thor: Ragnarok: A New Story. The story shifts between Hulk and Thor. Hulk from the moment he enters the Quinjet and gets pulled through a wormhole, to his first day on Sakaar, showing how he got captured by Valkyrie and his first two tournaments.
Thor's story takes place right before Thor: Ragnarok, showing how he arrived on Muspelheim and why he is captured at the beginning. Basically, he was showing off trying to get Surtur to come for him, and eventually Surtur said he would only meet Thor if he left his hammer behind and surrendered himself as a prisoner.
The epilogue takes place just before the party scene in Age of Ultron and is about Thor asking Banner if he remembered Hulk punching him after they defeated the Leviathan during the Battle of NY.
Timeline placements:
Thor: Ragnarok: A New Story - Prologue: May 4 2012, this is the scene of Hulk and Thor fighting the Leviathan together, ending with them standing in Grand Central Station and Hulk punching Thor. So it should go between
The Avengers #2 (pg. 13-14) and
The Avengers Chapter 18: "The Sacrifice Play" (2:04:31 - 2:09:30), I think.
Thor: Ragnarok: A New Story - Chapter 1: ''Just a few moments ago'' referencing Hulk getting on the Quinjet and flying away at the end of Age of Ultron. Should go after
Black Widow: Prelude #2 (pg. 8), April 2015.
Thor: Ragnarok: A New Story - Chapter 2, 4, 6 and 8: November 2017, Thor is on Muspelheim, just before
Thor - Ragnarok Chapter 1: "The Great Prophecy" (0:00:00 - 0:06:19), however it is mentioned he was fighting for hours, so it could also be before
Avengers - Infinity War: Prelude #2 (pg. 1-3, 4-5, 7-13, 14-17)
(Can someone enlighten me why this is here? Are we assuming Wong and Strange are talking for the entirety of Thor Ragnarok chapter 1, 2 and 3?)
Thor: Ragnarok: A New Story - Chapter 3, 5, 7 and 9: So, this is a bit complex. The rest of the Hulk chapters take place on Sakaar, but we know time flows differently there. As far as I can tell, they all take place on the same day, the day Hulk arrived on Sakaar. Should we place it in May 2015, after
Captain Marvel - Prelude #1, "The Peacekeepers" (pg. 6)?
Thor: Ragnarok: A New Story - Epilogue: April 2015, this is right before the Avengers House Party starts. At least, that's what I figure, since it says ''BEFORE ULTRON'', and mentions ''There was no official business this evening, no world that needed saving'' which fits with them having just taken down Hydra and retrieved the sceptre. Banner also says ''before everyone gets here and this party goes full-on Stark.'' So, before
Avengers - Age of Ultron Chapter 3: "Avengers House Party" (0:21:23 - 0:33:00).
My consideration to put it on the timeline:
Yes: Basically the same as Black Panther: Aftermath. Also written by Steve Behling. No contradictions to existing media.
No: No objections, really.
Overall, I think these two stories are canon and should go on the timeline. The Black Panther Junior Novel prologue is something that could be left out, if it means we would need to put the entire novel on there.
Honestly, right now I really want it on the timeline, because it took me a crazy amount of time to do all this haha.
So with that said, huge props to
@Lebnyx and other contributors for this timeline. I mostly only look and care about the simplified order, but actually doing the work putting it on the complete timeline, I realize what an incredible work this community has put in there.