NBC
A projected 9 million viewers watched Donald Trump on "SNL."
According to the "equal opportunity" clause of federal communications law, if stations give time to one candidate, then his opponents may claim the right to the same amount of airtime. This doesn't include news programs.
According to Variety, NBC's New York affiliate, WNBC TV, filed its notice on Monday morning:
"Donald Trump, a candidate for the Republican nomination for President in the 2016 national election,
appeared without charge on NBC's 'Saturday Night Live' for a total period of 12:05 (12 minutes and 5 seconds) commencing at 11:39:11 PM ET on Nov. 7 and ending at 1:01:01AM ET on Nov. 8, 2015."
NBC Hillary Clinton appeared on the sketch comedy show for three minutes and 12 seconds.
The Washington Post reports that this occurs at the station level, not the network level. So, each independent station that aired Trump's "SNL" across the U.S. will have to file a notice and then fulfill valid airtime requests. Additionally, candidates must prove that they're valid contenders in each state where equal time is requested.
Earlier this season, Hillary Clinton appeared on "SNL" for three minutes and 12 seconds. Democractic presidential candidate Larry Lessig applied for equal time, but dropped out of the race before an agreement was made.
In the case when Al Sharpton hosted "SNL" in 2003, his opponent for the democratic nomination, Joseph Lieberman, requested equal time. Stations agreed to air part of one of his campaign events.
Trump hosted the NBC sketch show during November sweeps, a period when ratings inform advertising rates. Early numbers project that about 9 million total viewers tuned in, the show's highest ratings in years.