Hi Antoinette,
You can find the park hours including extra magical hours for the current month plus 6 months in advance on the Walt Disney World website.
To access this from the home page you will need to click on 'PARKS' followed by 'Calendar' which you will find on the left hand side of the page and then click on the box next to 'View Month' (which always shows the current month) and then select December.
As an example
HERE is the link to the page detailing the Magic Kingdom park calendar.
Once you have the calendar for December on your screen, you will then be able to click onto the individual days of your visit to see what time the park will open and close, the times of extra magical hours (if applicable) as well as the times of any parades or nighttime shows which are scheduled to take place that particular day.
I would expect the park calendars for December to be released at around the beginning of June.
Wishing you a magical trip!