I believe they just don't accept same day ADRs...when we were at DTD in the late afternoon at Disney Quest, I tried to get an ADR somewhere so that I could know that we would find seating...but found out that none of the DTD TS places accept same day ADRs...at least according to the CM that I spoke with for that phone call on that day. Luckily, it was about 3:30 pm and the restaurant was virtually empty...no prob getting in...I did a review, if you are interested...link in sig.
The Cafe does take ADR's (I'm not sure about same-day), but they don't follow the 180 +10 for onsite guests. It can be no more than 180 days exactly from the ADR date.