The release date of a film definitely closely aligns with a film's chances of winning the Oscar for Best Picture. The later in the year a film is released -- or, put another way, the closer the film's release corresponds to the start of Oscar voting -- the better the film's chances of winning the Oscar.
Let's look at the Best Picture winners since 2000 and the month of their release, for example...
2000 - Gladiator, May
2001 -- A Beautiful Mind, December
2002 -- Chicago, December
2003 -- The Lord of the Rings: Return of the King, December
2004 -- Million Dollar Baby, December
2005 -- Crash, May
2006 -- The Departed, October
2007 -- No Country For Old Men, November
2008 -- Slumdog Millionaire, November
2009 -- The Hurt Locker, June
2010 -- The King's Speech, November
2011 - The Artist, November
2012 -- Argo, October
In 13 years, three films won that came out between May and June. The other 10 winners were released between October and December. So, 77 percent of the winners in this time frame were released during the last three months before the Oscar nominations; four of the winners -- more than 30 percent -- were released in December, one month before the Oscar nominations; and eight of the winners -- more than 60 percent -- were released in the final two months before the Oscar nominations.
If we go back to the previous decade of the 1990s, the numbers look only slightly better for earlier releases. Half of the winning films in the 1990s were released in either November or December, 20 percent were released from August to September, and three films were released earlier in the year -- two of them in the summer from May to July, and one in February.
So, in more than two decades, only one single film ever won that was released prior to May, and only five other films were released prior to August. And the largest single block of films -- 15 films out of 22 -- were released in the last three months before Oscar nominations. Thirteen of 22 winners were released in either November or December.
If that isn't enough evidence to convince you that films have a far better chance of winning the later they are released in the year, look at the data for the most recent slate of nominees. Of the nine nominees for 2013, every single one of them was released between October and December. Not a single movie from the first nine months of the year got nominated.