The guests comprised a who’s who of that period in the 1920s and 1930s, when writers, actors, intellectuals and activists made Harlem a cultural hub of Black creativity and cultural ambition. Regina Andrews who was a young librarian at the 135th Street Library, recalls a party for author Jessie Fauset. Artist Ernest Crichlow recalls traveling as a young teen from Brooklyn up to Harlem and the sculptor Augusta Savage’s basement studio. While the folklorist-anthropologist-author of “They’re Eyes are Watching God” died in 1960, there are plenty of multi-hyphenates at the party. “Once Upon a Time in Harlem” turns viewers into time travelers but also invited guests, rightly grateful to be in the room.