Actually late December is also a very high
DVC demand time, just a little below early December, and you could have risks at 11 months out with a Dec 23 start date.
The risk of possibly being blocked out at 11 months out at WDW exists only for certain room categories and it is mostly a studio (and resulting 2BR lock-off) risk: AKV value or club level, BLT standard view, BWV standard or boardwalk view, VGF studios, Boardwalk GVs, and the GVs in the hospitality House booking category at OKW. If you will be seeking anything other than those, you will get what you want at 11 months out and walking is unnecessary. Moreover, even if seeking any of those, chances are likely still fairly decent for most at 11 months out for Dec 23 to Jan 1 other than AKV club level and the OKW Hospitality House area GVs. including because if you are blocked, it may be temporary, and a wait list could come through fairly quickly or just rechecking to see openings over a few days may work
The concept of walking a reservation is to lock in the room you want at least for your intended arrival date before 11 months out. Since reserving exactly 11 months out allows you to book only 7 nights initially, walking in your case would mean going on line at 8 a.m. Jan 17 and reserving Dec 17 to 24. Thus, you get your arrival night and block everyone else from getting the room you have for that night and nights thereafter, e.g., they cannot get the room you have reserved by booking a week on Jan 20 for Dec 20-27, because your room is already filled until Dec 24. Once you have your initial reservation, you then can drop and add nights to it by calling MS. The first call could wait until Jan 23, at which time you would drop Dec 17 through 22 and add Dec 24 through 29 with a Dec 30 check out date, and then add the last two nights you want on January 26.
You should note that there is also no guarantee walking will work because it depends on finding a date open when you can beginn to walk. For example, you might find on Jan 17 that Dec 17 is already gone in the room category you want. Since the third week of Dec is usually nowhere near as high in demand as the rest of Dec, that is not likely to happen but if it does, you just try again the next day to reserve Dec 18-25, and walk from there.