Passage: NBC's last major radio programming push, beginning on June 12, 1955, was Monitor, a creation of NBC President Sylvester "Pat" Weaver, who also created the innovative programs Today, The Tonight Show and Home for the companion television network. Monitor was a continuous all-weekend mixture of music, news, interviews and features, with a variety of hosts including well-known television personalities Dave Garroway, Hugh Downs, Ed McMahon, Joe Garagiola and Gene Rayburn. The potpourri show tried to keep vintage radio alive by featuring segments from Jim and Marian Jordan (in character as Fibber McGee and Molly); Peg Lynch's dialog comedy Ethel and Albert (with Alan Bunce); and iconoclastic satirist Henry Morgan. Monitor was a success for a number of years, but after the mid-1960s, local stations, especially those in larger markets, were reluctant to break from their established formats to run non-conforming network programming. One exception was Toscanini: The Man Behind the Legend, a weekly series commemorating the great conductor's NBC broadcasts and recordings which ran for several years beginning in 1963. After Monitor ended its 20-year run on January 26, 1975, little remained of NBC network radio beyond hourly newscasts and news features, and Sunday morning religious program The Eternal Light.

Question: How long was Monitor a success?
for a number of years