The Legendary Pokémon Ho-Oh has returned to Raid Battles in Pokémon GO. Originally scheduled to be available across the globe until June 7, it is now appearing until June 21. In addition, Shiny Ho-Oh has made its Pokemon GO debut and can now be caught by players. The iconic Rainbow Pokémon is appearing in Gyms across the globe alongside Latias and Latios, which will remain in their designated regions for a limited time.
Ho-Oh will only be appearing until June 21, so make sure to add this incredible Pokémon to your Pokédex before it hotfoots it away again.
Suggested Pokémon and tips to catch the Legendary Ho-Oh in Pokémon GO
Source: Pokemon.com
Pokémon Blog 
and around 21.06 “ho-oh will stay longer”
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Your source doesn’t say anything about the 21st.
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