Once your movie is ready to be released, the placement and presentation of your promotional material needs to be carefully mapped out.
That's because the timing & flow of information to your audience is critical.
If you can get an initial boost of enthusiasm from a large audience... that initial BOOST, will do so, so, so, so much for your movie in the long run.
Front-load your promotional work, so the movie can snowball into success later.
Remember: movies are 50% content, 50% distribution.