@jncndac -
@Fogs -
Agree completely, The Rules Of Time Travel was a complete mess handled terribly in this movie. A complete disaster which could have been avoided.

Establishing rules for how Time Travel in your movie works is important, they rush through an explanation via Professor Hulk and eventually we get a random cameo of the Ancient One to explain.

Her explanation is that;
• Rule 1; Destruction of the Infinity Stones would doom the universe
• Rule 2; Removal of ANYTHING from the past (unless returned to the precise moment it was removed) would result in an alternate timeline
• Rule 3; Drastic altering of the past would result in an alternate timeline

Rule 1 is broken;
The moment Thanos destroyed the Infinity Stones should have doomed the entire universe. Yet we are shown the universe doing fine (other than consequences of the snap) five years later.

Rule 2 is broken;
While the escape of Loki, death of characters from the past in the future, etc... would all result in alternate timelines. These are all 'fine'. HOWEVER, Captain America steals Pym Particles from the past and they cannot be returned because they are used and they are never implied to be replaced because they have a limited amount.

Rule 3 is broken;
Captain America returning and living out his life with Peggy would have created an alternate timeline, one in which he never returned to the present original timeline breaks the established Time Travel rules for the movie.

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If the movie had solely established 'Rule 2' then the Time Travel would have held up with the addition of a line of dialogue that he was given extra Pym Particles, but instead they purposefully added 2 rules which contradict the events of the start and conclusion of the film.

From the moment that Rule 1 is stated by the Ancient One, the movie has broken its own Rule given Thanos destroyed the Stones in Act 1.

@four20smoke -
"Where are they" - Cap America
"Answer the question" - Cap Marvel
"The universe required correction. After that, the stones served no purpose beyond temptation" - Thanos
"You murdered trillions" - Bruce
"You should be grateful" - Thanos
"Where are the stones?" - Black Widow
"Gone. Reduced to atoms" - Thanos
"You used them two days ago" - Bruce
"I used the stones to destroy the stones. It nearly killed me, but the work is done, it always will be" - Thanos

@Fogs - I think, rethinking of the Ancient One dialogue with Banner, when the stones are back in their place and time the timeline becomes stable. And that's the one where Cap is. Timelinae A. But since the events were changed quite drastically in the events i think there are atleast 3 different timelines now. B, where Loki escaped with the Cube and C, a timeline where Thanos was dusted, Nebula was killed and Gamora was plucked away from.

My major problem with the whole thing is. He had the time stones to bring back, but how can you bring back a stone that is not in the original shape of a Staff, a Cube, the power stone which is basically unstable to use if you're not a celestial being.. Sticking a stone back into Porter should be the only easy part. Though i'd like to see him face the Skull on Vormir.