We experienced the same problem with the specialty restaurants on Sirena in November, 2023. They open at 6pm (with lines waiting to get in) and are closing down by 9pm. If you go after 8pm it's a rush-job to get you out fast!
We like to eat later around 8:15 - 8:30 and we couldn't go anywhere except the MDR. Specialty dining rooms were dead and the buffet closed at 8:30. Fortunately, the Maitre D in the MDR was "Alex" and he took great care of us. He helped us "make the best of it."