Official statements from Nintendo and the Pokemon Company say that they will be released in "holiday 2016". Retailers like Gamestop might have further knowledge regarding this, but we don't know for sure; that date may or may not be accurate. At this early stage, a specific date may not exist.
Personally, I doubt that's the real date, because a December 31 release would be stupid from a business perspective. A release before Christmas is always optimal and is probably what you can expect from these games.