The still-untitled Avengers 4 is set to be the longest Marvel film to date, according to co-director Joe Russo. In a recent live stream Q&A, Russo stated, "The running time on Avengers 4 is currently sitting right at three hours. We'll see if that holds." For reference, Infinity War is the current record holder of "Longest Marvel film" at two hours and 40 minutes.
In response to a question about post-production, Russo revealed the team is roughly 50% done with the film. "We're about halfway through the editing process," Russo claimed. "We're really just scratching the surface on our VFX shots. There are more than 3,000 VFX shots in the movie; those require a lot of time and thought and energy and effort, and we're very early in the phase of getting VFX done."
Because of that timeframe, there is a very real chance that certain segments will be trimmed to avoid such a long duration. I don't think anything will be able to reduce the length of this film from being epic, but you'll need to plan your midnight showings accordingly so as to not return home at 4:00 am with work the next day.