That is EXACTLY what I did and got them on my first try ever, for the time I wanted! When I said "anytime", the CM said, "8 or 9, quick!" I said, "8!" This was also for the sunday of labor day weekend.
I go a step further. I do not depend on my clocks, so I get online and go to a website with the correct time (for Eastern zone). I sit and wait. As soon as the clock says 6:55 am, I hang up and start dialing. Once I got "in", I was on hold for just a few seconds before someone picked up- and yes, interrupt them.
the night before have your "script", pen and paper for confirmation #, phone number 1-407-WDW-dine, and credit card ready by the phone and computer.