Legendary Raid Hour

Legendary Raid Hour (originally known as Legendary Lunch Hour) is an occasional event that turns every available Gym to a specific tier 5 Legendary Pokémon or Mythical Pokémon Raid Boss during one hour. It usually occurs on Wednesday from 6 p.m. to 7 p.m. in local time zone. Unlike Special Raid Challenge, no additional free Raid Passes are given. Eggs start to appear in Gym 20 minutes before the Raid Hour if the Gym is not occupied by other Raid Battles or EX Raid Battles.

Trivia

 * If the boss rotation occurs on Wednesday, the Legendary Raid Hour will be skipped. Examples include July and, 2019.
 * It seems that Niantic is aware of this. No raid boss rotation has occurred on Wednesday afterwards.
 * The Mewtwo Raid Hour on September, 2019 was canceled due to technical issues. Niantic later announced the make-up Mewtwo Day will be held on October with move Psystrike. Two additional free Raid Passes could be received during the hour.
 * Legendary Raid Hours on March, and , 2020 were canceled in Japan, South Korea and Italy due to the COVID-19 pandemic.
 * Due to the same pandemic, Legendary Raid Hour was canceled worldwide from March until May.