I can confirm that, last week at least, they just issue all tickets from 10:30 am next to the old mill. We went there twice (on monday and tuesday) around 12 and all tickets for the day had gone, and yet there didn't seem to be massive crowds at DLP those days. Got lucky on wednesday morning but even though I was queuing before 11am, all slots earlier than 5pm had already gone. Incidentally, I had all our passes and tickets with me (with the 'hilarious' result of one of our party accidentally getting "locked out" of the park due to getting something from the hotel without his ticket and having to blag his way back in) but nobody asked to see any of them, they just asked me how many were in our party for the meet and stamped the appointment card with that number.