We had a bad experience with MTD on Ovation this summer. No reservations available until late, app was only occasionally working to try and make reservations. Huge lines on both the reservation side and the standby side.
Have a cruise on Enchantment in early November, the app shows MTD starting at 5:30. Possibly the smaller ships have more flexible MTD hours. We were able to book 5:45 My Time for all the nights except one where we selected 6:45. Done on the app and in my cruise planner. Fingers crossed that it all works.