Why 2017–18 United States network television schedule and 2017–18 United States network television schedule (late night) are similar

American late-night live television sketch comedy and variety show created by Lorne Michaels and developed by Dick Ebersol. Hosted by George Carlin on NBC on October 11, 1975, under the original title NBC's Saturday Night. Wikipedia

Time zone encompassing parts of western Canada, the western United States, and western Mexico. Places in this zone observe standard time by subtracting eight hours from Coordinated Universal Time (UTC−08:00). Wikipedia

American commercialbroadcast over-the-air television network. Flagship property of the Fox Corporation, and is headquartered at 1211 Avenue of the Americas in New York City, with additional offices at the Fox Broadcasting Center and at the Fox Television Center in Los Angeles. Wikipedia

American multinational commercial broadcast television network that is a flagship property of Walt Disney Television, a division of Disney General Entertainment Content of The Walt Disney Company. Headquartered in Burbank, California, on Riverside Drive, directly across the street from Walt Disney Studios and adjacent to the Roy E. Disney Animation Building. Wikipedia

American commercial broadcast television and radio network owned by ViacomCBS through its CBS Entertainment Group division. Headquartered at the CBS Building in New York City, with major production facilities and operations in New York City and Los Angeles (at CBS Television City and the CBS Studio Center). Wikipedia

American English-language commercial terrestrial radio and television network owned by NBCUniversal, a subsidiary of Comcast. Headquartered at 30 Rockefeller Plaza in New York City, with additional major offices near Los Angeles , Chicago (at the NBC Tower), and Philadelphia (at the Comcast Technology Center). Wikipedia