According to the highly connected folks over at Collider.com the first Watchmen trailer will be attached to The Dark Knight when it opens on July 18th.
They had a chance to interview Watchmen director Zack Snyder and according to them he gave non-verbal confirmation that we'll be getting our first look at what is sure to be an epic superhero movie with the upcoming Batman film. They have a couple of videos up that cover a lot of questions so I'd recommend you head over and check them out.
In other Watchmen news, according to SciFiWire Zack Snyder has begun work on trimming down what is at the moment a three hour opus to a more manageable size. It's not that he thinks it needs to be cut down, it's the studio:
"The balancing act for me is, you want the movie as tight as possible for, I don't know why, I guess so people can enjoy it. But for me, the hardest part is just, when is it not Watchmen anymore? I don't think that's a danger, but it's a thing that I am trying to be the gatekeeper of while other forces conspire to say, 'No. Length, length, length. Playability.' Whatever the hell that means."
It sounds like this is very much his "baby" and he's trying to protect it as much as he can.
He also went on to say that they'll be showing footage from the film at the upcoming San Diego Comic-Con next month (sweet!).
Watchmen opens March 6, 2009.