Each country (check this article to see what countries the app is out in) has its own internal minigame events. Minigame events in each country will start at the same time, which will not be the same time as every other country, due to time zone differences. Each country has its own internal leaderboard showing only players within that country, and matchmaking is also internal (players are only matched with other players from the same country).
NOTE: for the purposes of the game, the United Kingdom is considered 4 separate "countries". Scotland, Wales, Northern Ireland, and England each have their own internal minigames.