Just off Serenade (Aug. 12-17 2023) and can confirm the 5:00 pm main seating and 7:45 second seating seems to be here to stay.
I tried MTD for this first time and did not pre-reserve in the cruise planner. What's the point of "My Time" if you have to plan everything in advance? As soon as I got on board, I checked the app and the only MTD times available to reserve, for the whole week, were 8:15pm and later. Useless. Luckily, I eat late (7:30 or later) and the No Reservations line generally only took a few minutes to get seated except on night 1 when it took about 15.
Back to fixed dining next time.... but that 5pm early time. Ugh.