Hello, Danielle!
I've noticed over the years that Walt Disney World park hours, which include Extra Magic Hours, are usually available sometime around 6 months in advance. You should see those Extra Magic Hours posted in the very near future (probably a bit later this month.) Just check
Walt Disney World's Park Hours page, and be sure to check back again from time to time, as park hours are subject to change.
Be sure to have narrowed down which restaurants you'd like to try, including if you'd like breakfast, lunch or dinner; if you know how many meals you need to book and at what time of day, it's so much easier to just sort of shuffle those cards around to fit the EMH when they are announced.
I know it's hard to wait (this same wait happens to me every time) but you will still be just fine, especially in the middle of January, when crowd levels go down a bit.
Have fun planning! Be sure to send more questions as you think of them; I love to help!