Avengers: Endgame - 20 Things We Learned From The Director's Commentary

9. The Snap Initially Brought Everyone Back Immediately

One of the most important moments in the entire movie is The Hulk using the newly-minted Infinity Gauntlet to bring all of the dusted back to life, and the scene went through numerous iterations before everyone settled on the final one.

Markus and McFeely originally wrote a version where the dusted re-appeared immediately after The Hulk snapped his fingers, which would've led to Thanos attacking the heroes all at once.

McFeely notes that this prevented the "truly heroic reveal" that the final version of the revival ended up with, and that having the heroes all return at the end of act two would've undermined the threat of Thanos for the rest of the movie.