One of the key features of the Pokemon franchise is that almost every game is part of a pair, with slightly different gaming experiences. Each game has "version exclusive" Pokemon (to encourage trading) and has had different mascot Legendary Pokemon since Pokemon Gold and Silver. Occasionally, the games have had different plots as well, such as Pokemon Ruby and Sapphire featuring different villainous teams with opposing goals.
But Pokemon Sun and Moon has found a different way to keep the games unique for players. The two upcoming Pokemon games will be set 12 hours apart from one another. While Pokemon Sun's in-game clock will sync up directly to a player's Nintendo 3DS settings, Pokemon Moon will be twelve hours ahead, meaning that most of the gameplay will take place during different times of day.
Pokemon Moon players won't have a significant handicap while playing, as Pokemon Centers and other businesses in the Pokemon world are open 24 hours a day. However, Pokemon Moon players will probably do most of their catching at night, which means they'll encounter a different set of Pokemon. As in the real world, some Pokemon are nocturnal while others only come out during the day. For example, the Alolan Rattata and Raticate are nocturnal by nature, in part to avoid their daytime predators Yungoos and Gumshoos.
It's unclear how else the time difference will impact the two games. As the Alolan Region has an ocean setting, the time could affect the tides or when certain areas are available, forcing players to deliberately time when they travel betwwen islands.
Three different "times" were shown in a recent Pokemon Sun and Moon trailer, showing locations during the day, evening, and night. Recent generations of Pokemon games have also had a "morning" period, which might also make an appearance in Pokemon Sun and Moon.
Obviously, the time zone difference won't be the only thing unique to Pokemon Sun and Pokemon Moon. Both games will have their own set of exclusive Pokemon, including the Legendary Pokemon Solgaleo and Lunala.
Pokemon Sun and Moon will be released on November 18 in the United States and Japan, and November 23rd in Europe.