If you are up and online with the right order to book on the right days (even if your not a bit) you should not have that much of a problem.
We went last year from Dec 18 thru January 1st. I got everything I wanted. The only thing that gave me a problem was a Mama Melrose Fantasmic ADR and that was because they hadn't released them yet. We were in on
free dining for the whole trip and we had deluxe dining. So we ate at three venues most days including Christmas Eve/Day and New Years Eve/Day.
I booked the first 10 days at 180 days at 6am central time. Then it was a day by day after that for the rest of the trip. I only had to compromise on time by 5 minutes here or there.
So unless you are set on, absolutely MUST HAVE a very specific perfect typical meal time, you should be good.
There are some meals you want to book fiorst as opposed to going in date order though...Be Our Guest, Cinderellas (although it seems to be getting easier to book lately), Ohana to name a few.
We have visited during free dining for the past 7 or 8 years and I don't usually have much of a problem.
Good luck...and happy ADR-ing!