Wow this is amazing that you would put this off. Personally and I am usually right in saying this that the Christmas release would be the best idea and the best time to make money. In the market that Harry Potter targets that only compition is Twilight and that is a few weeks after Harry Potter. If you release it in the summer it will have to go up against Transformers again. The last time that it did I don't think that Harry Potter did as well as it should have. The only reason to hold it would be if you were going to change the whole format to 3D. Don't be stupid, there is more money in the November release!