Since its inception with the premiere of the original Iron Man film in 2008, the Marvel Cinematic Universe has become one of the most successful franchises in Hollywood history. Completely changing the industry with the shared universe model, the series currently consists of 14 feature films, plus a plethora of small screen content like ABC's Agents of S.H.I.E.L.D. and the Defenders shows on Netflix. Even though there's already plenty of material for fans to enjoy, the MCU feels like it's only just beginning as Phase 3 heats up and brings in more characters to eventually take the torch from the original Avengers.
Whenever a new MCU installment is about to hit theaters, it's become customary for viewers to marathon through the previously released movies in order to get properly hyped and jog memories about specific plot points that could connect. As one would expect, this is hardly something one can do overnight. As a matter of fact, it would take nearly an entire week to watch all of the MCU straight through with no breaks - so those planning something like this need to make sure they have some vacation time coming.
According to a post on the Marvel Studios Reddit, a viewer would have to spend 6 days, 15 hours, and 41 minutes to watch the whole franchise. This includes not just the movies and TV programs, but also the One Shots that used to be featured on the early MCU Blu-rays, the WHiH Newsfront web series, and even the Team Thor skits starring the God of Thunder and his new best friend, Daryl. In total, everything amounts to 9,581 minutes. For interested parties, Reddit also has a chronological viewing order chart that lists the full timeline from The First Avenger to Iron Fist.
Of course, even the most devoted MCU fanatic would be hard-pressed to pull this off, especially since it'd be borderline impossible to get through even a couple films without taking any breaks. This is mainly being brought up to illustrate how substantial the property has become over the past nine years, and it will continue to grow as Kevin Feige steers the ship towards Phase 4 and beyond. For comparison's sake, the Star Wars franchise (movies, plus Clone Wars and Rebels) can be binged in a far more "manageable" timespan of a little more than 4 days without breaks.
Just the big screen MCU is going to become considerably daunting in the near future. In the lead-up to Avengers: Infinity War, four new movies - Guardians of the Galaxy Vol. 2, Spider-Man: Homecoming, Thor: Ragnarok, and Black Panther - will all be released, adding roughly 8+ hours to the marathon (should they all end up being around two hours long). There will be some viewers who try to pull off an extensive Marvel viewing party before the ultimate team-up, but few will be able to cram it all in unless they do some considerable planning (or put their life on hold for a couple weeks).