New experiment: Mystery Bonus Hour
The Pokémon GO team is always looking for more ways to improve the gameplay experience.
Mystery Bonus Hour will feature—you guessed it—a mystery bonus!
Double catch Stardust was the bonus on Thursday, February 6, 2020, from 6:00 p.m. to 7:00 p.m. local time.
Another Mystery Bonus Hour with Double Catch Stardust is taking place on Thursday, February 20, 2020, from 6:00 p.m. to 7:00 p.m. local time.
Mystery Bonus Hour is skipping Thursday, February 27, but will return on Thursday, March 5.
Source: Official Pokémon GO blog