When Does the Film "The Avengers: Age of Ultron" (2015) Take Place?
"The Avengers: Age of Ultron" is a superhero film written by Joss Whedon [adapting "The Avengers" #55 & #57 v1 (1968) by Roy Thomas as well as "The Avengers" #19-#22 v3 (1999) by Kurt Busiek] that released April 22nd, 2015. So when is "Age of Ultron" set?
It takes place on the fictional Marvel Cinematic Universe timeline in the year:
We know this because in the film "Captain America: Civil War" (2016), during a scene which takes place in April of 2016 AD, Colonel Helmut Zemo whispers, "I've thought about nothing else for over a year." and Captain America/Steve Rogers replies, "You're Sokovian?" referring to the fictional country at the heart of this story and its aftermath.
2015 AD
We know this because in the film "Captain America: Civil War" (2016), during a scene which takes place in April of 2016 AD, Colonel Helmut Zemo whispers, "I've thought about nothing else for over a year." and Captain America/Steve Rogers replies, "You're Sokovian?" referring to the fictional country at the heart of this story and its aftermath.
2016 - 1 = 2015.
Furthermore, in "Captain America: Civil War" (2016) Iron Man/Tony Stark opines, "He decided to spend his summer" when referring to an event in this movie. That strongly implies this story is in the previous summer to the then-current spring: the summer of 2015 AD.
It must take place before the events of "Captain America: Civil War" (2016) in early 2016 AD and after the events of "Captain America: The Winter Soldier" (2014) in late 2013 AD.
In season 2 episode 20 "Scars" (2015), Agent Phil Coulson's statement "What's transpired over the last week is a lot to take in." tells us it has been one week since the intelligence was acquired in season 2 episode 19 "The Dirty Half Dozen" (2015) that sent the Avengers on their mission depicted in the opening scene of the film. Therefore the main action only covers less than a week in the summertime and it's all contained within the 2015 AD calendar year.
This Geekritique article and video examines its exact setting.
It is a chronologically midway film in the Marvel Cinematic Universe timeline and can be watched either at its timeline point or before “The Avengers: Infinity War” (2018) as an extended flashback.
