Time-travel is a difficult writing device because its tendency towards paradox creates a minefield of plotholes. Endgame adopts the brilliant strategy of not attempting to alter the past. It’s even said in the movie “Remember, bring everyone back to right now. Don’t change anything in the last 5 years”
Suppose one of the Avengers goes back in time. The instant they arrive, they create an alternate history and have to do their best not to alter it too much. Whatever they do won’t affect their own timeline, but it’s a common courtesy they extend to their alternate selves.
Assuming all goes well, events will play out in these alternate realities the same way they did in prime reality. These new branched timelines would have their own snap, their own time travel, and their own fractal branches. Not all the branches created have their own snap, as we’ll explore.
After some helpful feedback from some not-very-nice people on Reddit, I have since modified Roger’s timeline he created in 1950.
Also, shoutout to HISHE
Heavy spoilers follow