Yeah, I went to check the same thing in the app and the only time that showed up from my above example was 12:00, not the other times I saw on the website... and 12:00 is actually exactly what we already booked, lol.
I already knew not to trust the app but on Allure in October, we had dinner reservations one night and wanted to switch the time that day on the ship (we just decided we'd rather eat earlier or later, I forget, not important). The app showed no availability. We went to the restaurant and the hostess said every single 15 minute time slot was available and we could switch to anything we wanted. It was empty that night and my wife and I couldn't help but wonder how many people may have checked the app and said oh well, no availability, we won't eat there. We felt horrible for our wonderful server who clearly wasn't making many tips.