On which day did the attempted coup d'etat of 1991 in the Soviet Union begin?

The story behind the answer

August 19 is correct because the “August Coup” began that morning in 1991, when hardline members of the Soviet government (the GKChP) declared a state of emergency, placed Mikhail Gorbachev under house arrest in Crimea, and tried to roll back his reforms. The putsch quickly met resistance: Boris Yeltsin famously climbed atop a tank outside the Russian White House, rallying crowds and security forces to oppose it. The coup unraveled by August 21.

Remember it with this timeline: 19–21 August = the coup’s start and collapse; December 25 = Gorbachev resigns and the Soviet flag is lowered; December 26 = the USSR is formally dissolved. (December 24 is when Russia took