It was Saturdays that it was open til 9 last year. I don't know for sure that Sundays weren't open late, but Saturday was always the late night. If I recall correctly, Saturday was the only night to see Spectro, but they were doing Wishes on other nights.
I'm not booking a cruise, but I am ready to start making PS. You'd think they could have the hours out far enough in advance to book the 90 day meals and events. And my vacation goes into November so I've got even longer waiting for those hours to be released!