<Li> Jerry Lewis (52, mostly in the 1960s) </Li> <Li> David Letterman (51, mostly between 1980 and 1981) </Li> <P> Harry Belafonte guest hosted for a week in February 1968, becoming the first African - American to host a talk show . Among Belafonte's guests were Robert F. Kennedy and Martin Luther King, Jr . On April 2, 1979, Kermit the Frog was guest host . In addition, many other Muppets appeared for skits and regular segments: Frank Oz voiced Fozzie Bear and Animal, while Jerry Nelson performed Uncle Deadly, a Vincent Price - inspired Muppet during a segment with the real Price . </P> <P> Carson's contract, that took effect in 1981, reduced his work schedule to three nights a week, 37 weeks a year . "Best of Carson" reruns aired on Tuesdays in the weeks that Carson was hosting new shows . Monday night shows and shows for most of the 15 weeks that Carson had off were hosted by guest hosts . Due to the frequent need for substitutes, starting in 1983 permanent guest hosts were hired in order to give the program more stability . The permanent guest hosts were Joan Rivers (1983--86), then, after about a year where a wide range of guest hosts were used, Garry Shandling alternating with Jay Leno (1987 - 88) and finally Leno alone (1988--92) after Shandling left to focus on his Showtime series It's Garry Shandling's Show . Though the concept of using "permanent" guest hosts was fairly strictly adhered to, occasionally illness or some other situation necessitated a substitute guest host, as when David Brenner filled in for Joan Rivers on October 31 and November 1, 1985, when Rivers' husband was briefly hospitalized . </P>

When did the tonight show go from 90 minutes to 60 minutes