My 2 cents? Better safe than sorry! Better get the ADR, and if it ends up you have other plans you just cancel it, than hoping for a walk in and being turned down (allmost) everywhere you go.
I'm travelling solo 9-4/9/12, and had some problems and other places were real easy. I started calling in June.
Boma was a bit of a trouble to get an earlier than 7.30, but other than that; no probs with the date.
Le Cellier; forget about dinner. Lunch was possible after 3 times trying. (which I cancelled later on, doesn't fit my plans)
Coral Reef; forget about dinner. Lunch was no problem. I've actually just changed my ADR last sunday and could still pick a lot of dates and times.
Chef Mickey; big problem for both diner and breakfast. Only 7 am breakfast, which didn't suit me. Only dinner option; 9 pm at the day of my arrival. Didn't feel relaxing at all, I want a "no need to do" day in case I am simply to tired from the flight. Learned on the DIS they do lunch for certain dates during
free dining. Called and could pick any day, any time.
The Plaza (dinner) and Christal Palace (dinner and breakfast); no problems. Could pick whatever, and changed them around quite a few times.
Sci-Fi; lunch fits my plans best, and had no problems picking date and time this last sunday.
Cape May Cafe; no problems again for dinner.