system
Given the following post, respond as if you're commenting on Reddit:
human
[MCU] Yet another Endgame question

Why didn't they go back to the brief period  (20 days or so?) between the snap and the stones' destruction by Thanos? They had the complete gauntlet in place, a weakened Thanos, and the element of surprise. Even an injured titan is no joke, but it seems a lot less risky than splitting and going on an extended time heist on several different planets.

Edit: to be clear, I'm not asking whether it's a viable option or not *objectively* speaking, but why it didn't come up in their own mind. From the A's point of view, confronting gauntleted Thanos is viable (since they were ready to do it anyway), and time shenanigans aren't an issue (since Banner didn't hear the Ancient One's spiel).
gpt
A couple of things:

First and foremost, they only had enough Pym Particles for one trip; there were no do-overs, and that means they had to be certain that their plan would work. That makes the next points critically important.

If they try to take the gauntlet from Thanos, it means a fight, and there's a significant chance that the Avengers lose. Yes, they had Thor with Stormbreaker and Captain Marvel, but Thanos had the full Infinity Gauntlet. Fighting him was absolutely not a sure thing. Hell, they barely beat Thanos with *no* Stones at the climax of *Endgame*; taking a fight to him when he has all six is a suicide mission.

Also, the Avengers didn't know when Thanos arrived on Garden. He probably went there directly after the Snap, but they couldn't be sure, and that means they would be gambling with the fate of half of all life. If the Avengers arrive too early, Thanos might detect them and run. This means they've lost their only shot at ever getting the Stones. Or, he might launch an attack, where he has the advantage of surprise.

The Time Heist is risky, but not as risky as fighting a near-omnipotent maniac who will respond to your attempts to undo his Great Plan by unmaking the universe.