Niantic had previously confirmed that it would release Harry Potter: Wizards Unite on June 21st. However, if you live in of these two countries, you will be able to play the game a day early on an iOS or Android device. Niantic is likely opening up the game to early adopters a day before the official launch so as to prevent server overloads that were experienced with Pokemon Go.
Potterheads in the United Kingdom and the United States can now get Harry Potter: Wizards Unite on their iOS and Android devices. They join users from Australia and New Zealand who have had access to the game courtesy of a beta test of sorts for a few weeks now.
Given the sheer popularity of the Harry Potter franchise, Niantic might be expecting a massive influx of players on the launch day. In order to mitigate any server overload issues, it has decided to roll out the game a day earlier for players in the UK and the U.S.