Just visited, the museum is open all year round, open every day, 8:30-18:00 from April to September, 8:30-18:30 from October to March, it is recommended to book tickets online in advance to be more favorable.
It used to be open every day, but now I don’t know if it will be open during the epidemic, but judging from the local government’s supplementary Cambodian New Year holiday, it should be open.