Question: When did the heavyweight boxing championship match, for which the Zaire 74 concert was intended to be a major promotional event, actually take place?  
Sentence (from "Zaire 74"): Zaire 74 was a three-day live music festival that took place on September 22 to 24, 1974 at the 20th of May Stadium in Kinshasa, Zaire (now Democratic Republic of the Congo).
Relevant evidence: Yes