Marvel committed dates for 5 films -- Iron Man 3, Thor: The Dark World, Captain America: The Winter Soldier, The Guardians Of The Galaxy, and the untitled 2nd Avengers film -- and have also hinted strongly at Edgar Wright bringing Ant-Man to the screen as well. All 6 films, presumably have to be in the theater by May 1st 2015. So between now and then, they have a little under 3 years. The math, in terms of when they actually have to shoot each film, should go roughly like this:
Iron Man 3
5-6 month shoot
April, 2012->Sept, 2012
Release Date: May 3, 2013
Thor: The Dark World
4-5 month shoot
Sept, 2012->Dec, 2012
Release Date: Nov 8, 2013
Captain America: The Winter Soldier
4-5 month shoot
Jan, 2013->May, 2013
Release Date: April 4, 2014
The Guardians Of The Galaxy
5-6 month shoot
May, 2013->Oct, 2013
Release Date: Aug 1, 2014
Ant-Man
4-5 month shoot
Sept/Oct, 2013->Jan, 2014
Release Date: April 3, 2015
The Avengers 2
5-6 month shoot
Jan 2014->June 2014
May 1, 2015