The Defenders has just added eight Netflix episodes of content to the overarching Marvel Cinematic Universe for a total of about seven hours worth of expansion to the world.
Including The Defenders, the entire Marvel Cinematic Universe would require seven days, eight hours, and three minutes to watch. The number was calculated by a fan who organized the entire chronological order of the Marvel Cinematic Universe.
Beginning with Captain America: The First Avenger, the order moves on to 18 episodes of Agent Carter, before being followed by several flashback and miscellaneous sequences attached to Marvel Cinematic Universe titles. The first film to follow is Iron Man, then Iron Man 2 and The Incredible Hulk, which are followed by a pair of one-shot films before Thor and The Avengers. Of course, this is all considerably different from the release schedule, and Phase 1 of the Marvel Cinematic Universe is rounded out by the Item 47 one-shot.
Phase 2 kicks off with Iron Man 3 and its All Hail The King one-shot, and it's heavily filled by episodes of Agents of SHIELD, which first aired in the aftermath of The Avengers.
The list goes on, including Guardians of the Galaxy, and eventually introducing the Netflix characters of Daredevil, Jessica Jones, Luke Cage, and Iron Fist (not necessarily in that order). It all leads to The Defenders episodes which debuted on Netflix over the weekend and directly precede The Inhumans IMAX premiere on September 1st.
The Marvel Cinematic Universe launched in 2008 with Iron Man but extends back as far as 1942.
Moral of the story: get a very, very, very comfortable chair and a bottomless bucket of popcorn if you're planning on watching the entire Marvel Cinematic Universe.