The big caveat is the tentpole's running time of three hours and 58 seconds. That means a reduction in showtimes. So far, Disney and theater owners appear to be making up the difference by adding additional screens and showtimes. And online ticket service Fandango says 4,000 shows are sold out.

The box office is in sore need of good news. Domestic revenue is running 17 percent behind the same corridor last year, although many believe Endgame could be the first of many 2019 juggernauts (many of them from Disney).

Avengers: Endgame is directed by the Russo brothers, who shot the movie back-to-back with last year's Avengers: Infinity War.

The nostalgia factor is running hot. Not only is Endgame a direct sequel to Infinity War, it's the culmination of the previous 21 titles in the Marvel Cinematic Universe, a blockbuster series of films that commenced with Iron Man in 2008 and established Kevin Feige's Marvel Studios as best in show.

Avengers: Infinity War, which ran two hours and 29 minutes, is the current record holder for biggest global opening ($640.5 million) and biggest domestic launch ($257.6 million) after stealing the crown from Disney and Lucasfilm's Star Wars: The Force Awakens ($248 million), not adjusted for inflation.

A big difference this time out is that Avengers: Endgame is opening day-and-date in China, unlike Infinity War, which debuted to more than $191 million in the Middle Kingdom two weeks after rolling out in much of the rest of the world.

Some analysts believe Endgame could take in $250 million in its launch in China, where it opens Wednesday. That potentially means that the pic could cross $1 billion in less than a week in release.

Around the globe, Avengers: Endgame has shattered presale records, including selling more advance tickets in its first 24 hours than any picture in history.

April 23, 1:30 p.m. Updated with Fandango sold-out shows.