Pokémon Gold and Silver introduced a day-night cycle that changed the game world according to time.
Released for the Game Boy in Japan in 1999, the games tracked the player’s clock and divided the day into periods such as morning, daytime, evening, and night. This affected which Pokémon appeared, when some events occurred, and how certain locations looked.
The system made the world feel more persistent than the fixed-time structure of Pokémon Red, Green, Blue, and Yellow. For example, some species were easier to find at night, while other encounters were associated with daytime. The clock also supported time-based events and influenced features such as evolution for certain Pokémon.
Later Pokémon games expanded the idea with weather, seasons, and broader real-time systems. Those features are related but distinct. Gold and Silver are specifically remembered for bringing a functioning day-night cycle into the main series, making time an important part of exploration.