When to sell the shares is a trickier question to answer - it depends more on the individual movie and what its prospects for opening weekend are.
If the market thinks the movie is under-valued, the price will continue to go up. If the market thinks that the movie is over-valued it will trend down. I think traders start looking seriously at upcoming movies about 4-6 weeks before release - though it can depends on other factors, like when the trailer comes out, what the audience response is, time of year, how much money is in the market etc.
With Planes, I sense a bit of uncertainty. It's a sequel to a Pixar movie, but it's not a Pixar movie, but audiences will probably think it is. It was originally STV but now it's opening in theatres but so did Toy Story 2. It's current price suggests an opening weekend of $50M+, which is possible in August, but rare. Etc...
With Hunger Games 2, I don't have any doubt. An expected huge opening weekend should mean it continues to go up in price until it opens (though it will probably have a blip in the traditional September market collapse) However, it's getting close to the price point where there's not a lot of money to be made. With a port your size you would make more money by selling out and using the cash to make more profitable short-term investments. Then you can jump back in on HGAM2 before opening weekend. But if you're playing purely long-term that's fine too.