Can't say what it will be like when you book, but I definitely found it more difficult to get earlier ADRs when I was booking for my September trip. I was online at 6:00 am on the dot on my 90+10 day, and still ended up with a 7 pm dinner (1900 park fare) and 1:30 pm lunch (Akershus).
And, of course, some restaurants are difficult no matter what time you're looking for. The only time I've ever seen an open dinner spot for Ohana during my week was for 9:30 pm! And trust me, I check at least twice a day.
Now, I am going during free dining and it seems to be a busy week, too (Sept. 27-30), so that may make a difference. I hope you have an easier time of it!