How many minutes does it take to interview Katharine Hepburn, Paul Simon, Robin Williams, Johnny Cash, Lena Horne, Vladimir Horowitz, Laurence Olivier, and more than 20 other legendary entertainers? If you're 60 Minutes, it takes about 120. CBS' long-running news program will broadcast a two-hour special, 60 Minutes: The Entertainers, featuring highlights from the show's best celebrity profiles over the past 23 years. ''We have a gold mine,'' says Don Hewitt, 60 Minutes' executive producer. ''We have a video history of entertainment over the last two decades everybody from Johnny Carson to Liza Minnelli to Jackie Gleason.'' One of Hewitt's favorite clips: a 1988 interview with George Burns, in which the veteran comic visits late wife Gracie Allen's tomb at Forest Lawn Cemetery in Los Angeles. (Burns to Allen: ''Googie, this is Ed Bradley. We're going to be on 60 Minutes. We're working together again!'') How does 60 Minutes decide which celebs to profile and which to skip? ''We try not to do the rock star of the week,'' says Hewitt. ''We only interview stars of durability. Madonna doesn't interest me at all. She's a fad of the moment. She's no Elvis. She isn't even the Doors. Somebody once suggested we interview Meryl Streep. We turned it down. I told them, when Streep becomes as big a star as Hepburn, we can talk.''