According to a listing on Fandango, Avengers: Infinity War will run for 156 minutes, or 2 hours and 36 minutes, although it could be shorter minus the credits. Previously the longest Marvel movie belonged to Captain America: Civil War, which we guess was like a pseudo-Avengers movie that brought multiple superheroes onto the big screen.
The movie’s co-director Joe Russo also adds that chances are Thanos will have the most screen time which makes sense given that he’s the movie’s primary antagonist. Russo also adds that Thor could also have quite a bit of screen time where he said, “I think you’ll find that Thor has a really interesting arc in the film. He hasn’t been at the forefront of other Avengers movies but he certainly has a very important role in this film.”
In any case it’s something worth taking note of if you plan on watching the movie. Avengers: Infinity War is currently set for a release on the 27th of April, 2018.