Which Pokémon games first introduced a real-time clock tracking the time and day of the week?

Pokémon Gold and Silver first introduced a real-time clock that tracked the time and day of the week.

Released for the Game Boy Color in 1999, the games formed Generation II and expanded the Pokémon world with the Johto region. Their internal clock changed the game world according to the player’s actual time, creating morning, day, and night periods as well as a weekly cycle.

Time affected which Pokémon appeared, when certain events occurred, and how some characters behaved. The system made the world feel more persistent than the fixed-time environments of Pokémon Red, Green, Blue, and Yellow.

The feature is sometimes confused with later day-and-night systems because subsequent games expanded the idea with seasons, weather, and more detailed schedules. Gold and Silver established the original real-time foundation. They also introduced 100 new species, Pokémon breeding, held items, Pokémon eggs, and the ability to revisit the Kanto region after completing the Johto adventure.