When I was on my cruise aboard the Inspiration last year. They seemed to only have one big midnight buffet. I think that it may have been called the Grand Gala Buffet like Billy mentioned. I have also heard it called The Midnight Chocolate and Dessert Lovers Buffet. And BOY! You DO NOT want to miss it!
That is unless you are not the least bit of a sweet tooth!
I believe they may have had other smaller themed buffets on other nights at an earlier hour. A Caribbean/Mexican food buffet for example.
Most of the cruise lines are doing away with the late night buffet. They will have a cafe or small portion of the buffet area open with limited service. Food is always available. Room service is round the clock.