There's a lot of correct information up here, but then some incorrect assumptions.
Flights arriving before 11:00 p.m. will have their DME luggage delivered to the resorts that night/early morning. The approximately 11:00 p.m. cut-off is a cut-off time for airplane landings, not a cut-off time for any luggage operations at all.
Let's look at pre-11:00 p.m. arrivals. Disney says to expect your bags to get to your room about 3 hours after you arrive at your resort. So if you land at 7:45 p.m. (assuming your flight's on-time), you can count on being at your resort by 9:15 p.m. This means to expect your luggage by about 12:15 a.m. Again, it's not that all luggage freezes at 11:00 p.m. or turns into a pumpkin or anything, it's that luggage at the airport won't be processed/sent out for delivery after 11:00 p.m. If your luggage already left the airport before 11:00 p.m., then you will be eligible to get it that night and NOT have to wait 'til morning (if the luggage from a 7:45 p.m. arrival hasn't left the airport by 11:00 p.m., that's a very big delay/problem in its own right). So to clarify, it's not that luggage delivery ends at 11:00 p.m., it's that luggage processing at the airport stops by 11:00 p.m. If it's 11:00 p.m. and your bags are already en route or are already at your resort, you will get them that night unless you specify otherwise.
Same thing with luggage from a 9:00 p.m. flight. Unless there is some sort of drastic problem at the airport, that luggage will be delivered to you that night, you won't be forced to wait 'til morning. The reported average time from deplaning to resort drop-off is 70 minutes, but I always liek to use 90 minutes in my little examples, just to allow for little delays. So with a 9:00 p.m. arrival, figure you're at your resort by 10:30 p.m., and figure your luggage could be to you by 1:30 a.m.
A flight scheduled to arrive at 11:30 p.m. will have its DME luggage spend the night at the airport. It will be sent out on the first DME delivery truck of the morning. I don't recall anyone in-the-know reporting a definitive time for that, but I think I recall reading something about 7:00 or 8:00 a.m., but please don't quote me on that.
NOW ...
You don't NEED to accept your luggage in the middle of the night if you don't want to. You can ask at the front desk AND with Bell Services to have your DME luggage held 'til morning.
I forgot to do that, even though I was on the DIS for months recommending that other people do it ... but I just was so excited to be there it slipped my mind. We landed around 10:00 p.m., got to POFQ around 11:00 p.m. (56 minutes from deplaning to POFQ drop-off), so we should have expected the luggage by around 2:00 a.m., 3 hours after our resort arrival. We packed for the night and next morning in our carry-ons, as I'd planned to have the luggage held 'til morning. As I said, I forgot. Our phone rang at 1:16 a.m. (the visual image of that alarm clock is seared into my brain) ... it was Bell Services asking if we wanted our bags now or in the morning. I mumbled something about morning, and don't remember seeing the clock change to 1:17 a.m. I woke up around 6:30 a.m., called Bell Services, and our bags were at our room within 5 minutes, no exaggeration!
The most important point is that even if you aren't using DME ... heck, even if you're flying somewhere other than Orlando!!! ... you should pack a carry-on with your first 24 hours of supplies just in case the AIRLINE delays your luggage. Think of it as a sort-of
travel insurance -- in the unlikely event of a luggage delay, you can still have fun at he start of your vacation!