When Sylvester Stallone ended his stormy on-again, off-again commitment to star in producer Robert Evans' "Cotton Club" by pulling out of the project completely two months ago, the future looked questionable for the $20 million story of the Harlem nightclub. But Evans has now made a splashy announcement that he has signed Richard Gere and Gregory Hines to star in the film, which will be directed by Evans from a script by "Godfather" and "Superman" screenwriter Mario Puzo. Covering the nightclub from the end of World War I to the end of the depression, the film will be shot on what Evans terms "European hours," from 11 a.m. to 7 p.m., without the standard early morning start or the usual frequent breaks; the producer says that schedule works better "to keep the energy level high" on the 30 dance numbers in the film. The unions, though, have never allowed such a schedule to be used in an American movie project, and while Evans says he has had no objections from those he's talked to so far, he also vows to move the project to Mexico if he can't do it here. Hines, who just left his starring role in "Sophisticated Ladies" after playing the part on Broadway and in Los Angeles, will be doing extra duty on the film, though he'll only be paid for his acting and dancing. Free of charge, he's also going to serve as the film's choreographer and to line up blacks to play half of the movie's 150 roles (the crew, Evans says, will also be 50 percent black). Hines promises to round up every famous tap dancer he can find for the project, and the Harlem-bred actor/dancer explains his generosity with a simple, "I just had to be in that film."