I feel like this is the best that we can do (well, I'm sure more accuracy can be added about exact days and such):
3,000 BC - Apocalypse builds pyramids (DoFP)
1832 - 1845 James Howlett born, kills stepfather, runs away with Victor (XMO:W)
1861-1865 James and Victor fight in Civil War (XMO:W)
1917-1918 James and Victor fight in WWI (XMO:W)
1944 Erik Lehnsherr taken to Auschwitz & experimented on (XM:FC, XM)
Charles Xavier meets Raven Darkholme (XM:FC)
June 6 - James and Victor involved in D-Day (XMO:W)
1945 James fights in the Pacific Theatre and is captured
August 6 - James saves Yashida when Nagasaki is bombed. (TW)
1959 XM:FC prequel comic
1962 The rest of XM:FC (surrounding the Cuban Missile Crisis in October)
1969-1971 James and Victor fight in Vietnam, shot by firing squad, survive, recruited by William Stryker for Team X (XMO:W)
1972 James (Logan) quits team X (XMO:W)
1973 The past part of DoFP (surrounding the Paris Peace Accords on January 27) ***TIMELINE SPLITS***
ORIGINAL TIMELINE
1979 The Rest of XMO:W (leading up to the Three Mile Island Accident on March 28 )
1986 Xavier and Lehnsherr visit Jean Grey (Magneto evidently was released or escaped prison at some point and rejoined with Xavier) (XM:TLS)
1996 Young angel cuts off his wings (XM:TLS)
2003 The rest of X-Men
X2 Prequel Comics
X2
2005 X-Men Video Game
2006 The rest of X-Men: The Last Stand
2013 Main story of The Wolverine
2015 Airport scene from TW
2023 The future part of DoFP ***TIMELINE SPLITS SEVERAL TIMES AS KITTY GOES BACK IN TIME***
NEW TIMELINE
1983 X-Men: Apocalypse (I haven't seen this)
1990s? X-Force (not yet made)
??? New Mutants? (not yet made)
2018-2020?Deadpool (I haven't seen this)
2023 The ending of DoFP
Future? Wolverine 3 (not yet made)
There are lots of continuity issues, such as EVERYONE's age making no sense and/or multiple versions of the same character. If we put the young jean grey and angel scenes at 30 years before The Last Stand (rather than 20 and 10 years before), then they both fit with Apocalypse better, but it puts them both around 40 in the original movies. I think the nature of these films is such that you have to ignore everyone's ages.
There is also lots of viral marketing that adds details about history, but I didn't bother to add those.