Okay, let's take a look at the evidence we have:
December 31st 1999/January 1st 2000 -
fixed date, Tony at the conference in Bern, meets Yinsen, Killian et al. (IM3)
February 14th 2008 -
fixed date, Killian find candidates for the Extremis program (date shown in IM3)
2010 - IM (6 months before IM2 as stated by Senator Stern in IM2)
2011 - Fury's big week (Fury mentions in TA that the events of Thor happend 'last year')
2012 - the Battle of New York/ the Incident (year given in AoS S2E06 A Fractured House)
December 2012 - IM3
September 9th 2013 -
set date, Grant Ward is promoted to Level 7 and gets a new ID batch with it's date clearly visible in AoS S1Eo1 Pilot
November 2013 - Thor The Dark World (Darcy states that Thor was gone for over 2 years since the events of the first Thor, set in 2011, A calender can be seen in the movie saying November)
First Half of 2014 - Winter Soldier (Falcon states they're looking for the Winter Soldier for two years in Civil War, given that Rogers says he's 95 in TWS it has to happen before July 4th)
2014 - GotG, Got2 v2 ('34 years later' than the '1980' opening scene of the first movie)
January 6th 2015 - This google+ post
May(?) 2015 - AoU (in CW it is mentioned by Tony that 'Spencer decided to spend his summer in Sokovia' which is when the battle of Sokovia happend. Zemo says he spent over a year planning his revenge. So early summer, really, May probably
July 17th 2015,
set date, Scott Lang is released from prison (WHiH)
December 2015, Peter Parker was bitten by a spider (He had this power for 'six months' in CW)
May 3rd, 2016 -
set date, WHiH coverage of Lagos Incident
June 2016 - Vienna International Center bombing, stated as 'one month after Lagos' (or Lagos was stated as 'last month' something along that line)
August or September 2016 - Start of Homecoming, judging by the 'two months later'. Assuming CW happend late in June, September is more likely, given that August is an akward time to go to High School (as is June for having homework, frankly, but I have no idea when summer holidays in the US usually end)
that's the bits that are working, now for the onscreen bits that didn't work:
2020 - the events of Homecoming (8 years after the Battle of New York)
edit: rereading this, I noticed I forgot Visions line in CW about the '8 years since Tony Stark announced himself as Iron Man' which, going by all other evidence surprisingly doesn't work neither with earlier given dates. So either IM is set in 2008 instead of 2010 which doesn't work with the dates given in TA and IM2 or CW is set in 2018, which means, since Cap is still 95 in TWS, Falcon and Cap started looking for Bucky in 2016, two years after the events of TWS and after AoU. This would also mean that the date of the WHiH footage for CW is wrong by 2 years.
It still doesn't make any sense in relation to the 2020 date of Homecoming, though. There's still a gap
2016 seems to be the year Dr. Strange started his training under the Ancient One, I can't remember any exact dates given in canon. IF Strange started experimenting with the Eye of Agamoto around May/June 2016 however, there might be an in universe reason for both Vision's 'eight years' and Toomes' 'eight years', as in
Strange broke time completely in early summer 2016