Maybe this will help-
Went last Christmas (2016) had rooms at Coronado, My room was December 9-15. Kids rooms were December 10-16.
Free dining started December 10- so the kids rooms (these are young adults) I was able to modify online and they were done. Because December 9- did not fall under the free dining plan, I could not modify online. I ended up doing a room only for the 9th, then booked a new room December 10-15 to get the free dining.
The frenzy will be the first day the free dining goes live- I was on the phone for 3 hours on hold (as were many) and ended up being disconnected. I called again a day later and was able to get the 10-15 booked.
When we arrived- we did not use much of the QS credits thinking we would run out to soon-but really did well with the TS credits because we did heavy character buffets etc. Lesson learned- use it daily-ended up converting QS to snacks and used them for Mickey Mouse lollipops for the younger kids-100 bucks worth
The rapid refill mugs are excellent for morning coffee and when we did get breakfast at the resort- we made sure we got a bottled beverage that is included with the QS breakfast to take to the parks (use refill mugs for breakfast beverage)
Note- the resorts do fill up, but at full capacity on the resort side does not mean full at the parks.
If you do stay at the value resorts and get the QS dining plan- upgrade and pay the difference to get the dining plan- little money and 1 TS credit per person per day.
The free dining was a win for us as we had 7 people- big savings. If we did not have the kids and extra rooms- I would hunt for the room discount.
Lastly- The free dining plan offer- took quite a bit of time to run out of rooms. I do remember trying to add on an additional room in July-for some friends and it was still available.