Moviestocks that open wide adjust on Sunday, based on how much they open over the weekend.
They halt on Saturday at 6PM Pacific, and then freeze through Sunday, unfreezing after they are adjusted.
USUALLY, it takes the money earned Fri - Sunday, and multiplies it by 2.7. So if it made $10 million, the stock would adjust to $27 when it unfreezes. Basically, you're betting on whether the movie will exceed projetions or fall short.
IN THE CASE OF AMERICAN SNIPER, and for other movies with varied openings, or around holiday weekends, etc., a different forumla is used. You can see this by going to the 'NEWS AND EVENTS' tab and selecting 'MARKET CALENDAR'. From here, you can scroll down to Saturday and see it metioned that it will halt trading at 6pm, this is when it freezes. Click "NEXT WEEK' at the top to go to Sunday, Jan 18, and you will see the stock shown with its adjust formula. In this case it is
(Previous Box Office + (3.0 * Box Office Fri-Sun)):
This means that it will take the earnings from Fri-Sun, and multiply them by 3, AND THEN add on the money that was made earlier in the week from earlier theater releases.
Finally, you can keep an eye on projections and, once Friday night gets going, you can really begin to see where it is tracking. You often see projection and tracking posts on the Movies forum.
Good luck.