https://www.gamespot.com/articles/pokemon-go-legendary-moltres-returning-this-saturd/1100-6461608/

Pokemon Go players will soon have another chance to capture the Legendary Pokemon Moltres. As a reward for completing the Global Challenge during last week's Safari Zone event in Yokosuka, Japan, the Legendary bird will return to Raid Battles this Saturday, September 8, but it'll only be around for a very limited time.

Like Pokemon Go's Community Day events, the upcoming Moltres Day will only last for three hours, during which time you'll be able to encounter the Legendary Fire-type Pokemon as a Raid Battle at Gyms. The event will occur around the world, but the hours will vary region by region. You can see exactly when it takes place in your region below.