Hey Melissa! Whereya been?
< jk >
January 2020, like snowmedic says, hasn't been loaded online and won't be until 2020 rates are announced this summer sometime. However, you can, as he says, call and book January 2020 at 2019 rates which will later adjust to the later 2020 rates once announced. The 500 day rule does apply (you can book over the phone up to 500 days from the check OUT day from WDW).
There are some difficult times in January to book even well in advance (my purpose for posting).
First, is right after New Years. Still got that holiday no-work, no-school crowd wanting to go to WDW. Book well in advance.
Second, during the WDW Marathon week 2020 which is Jan 8-12 (Wed-Sun). Been there, done that (a couple times). The resorts book up for the run weekend early. Parks aren't that much busier but reservations at the resorts fill up (including the Fort) about a year in advance.
Third, MLK weekend (3rd Monday of the month usually) means a three day weekend for many which means the resorts (and parks) are busier that weekend.
So book early, book now, and if you can avoid the three times above, so much the better.
Bama Ed