What you do is try 9:00. No availability. Try 9:30. No availability. Keep doing this until something pops up. Take ANY available time, even if you can't use it. Then try to modify that time, using the same technique. Modifying is much easier for some reason.
You can get pretty much anything this way. I got Flights of Passage on 2 different days, although it took quite a lot of refreshing over several says. At the parks, you should be able to get most rides within 15-30 minutes of trying. It's a good way to pass the time waiting in line.