I've never been to WDW, so I don't know how its been in the past - I can offer my experiances though
I called right at 7am on my 90 day mark....I got a 9:55am ressie for the day after I get there - YAY.
After further review, I figured I would want a later breakfast because I didn't want to waste those morning hours when the parks are emptier - so I called and scored a 10:35 reservation - WOO HOO
What I really wanted was an 8am ressie on one of two days. I was able to check online yesterday and scored an 8:05am ressie for the last day I am there (and I just cancelled my 10:35 ressie in turn). So in my experiance, its been trying, but I didn't give up! I actually ended up with exactly what I was looking for.
I would say, be flexable with your days and call right at 7am (or better yet, check online).
Good luck