Twilight as released on 21st of November 2008
New Moon was Released on the 20th of November 2009
Eclipse was released on 30th of June 2010
Breaking Dawn Part 1 was released on 18th of November 2011
Breaking Dawn Part 2 is going to be released on 16th of November 2012
So have you noticed the pattern, Eclipse was the only movie to be released not in November. It was released in June for some reason, maybe to break the pattern.
Between Twilight and New Moon there is exactly 364 days apart from each other, while New Moon and Eclipse there is 7 months between the two of them, but with Breaking Dawn: Part 1 and Eclipse there is 18 months a part from each other and Breaking Dawn: Part 2 and Part 1 are almost a full year a part like Twilight and New Moon was.
Sorry if I am confusing you, but I have just figured out the pattern on their release dates.