Which main-series Pokémon games first introduced a real-time clock system?

Pokémon Gold and Silver were the first main-series Pokémon games to introduce a real-time clock system.

The feature uses the Game Boy Color’s internal clock to track the time of day and day of the week. The in-game world changes depending on when the player is playing, making some Pokémon and events available at particular times.

The system affected more than scenery. Certain Pokémon appeared at different times, some trainers called the player on the Pokégear, and scheduled events could occur on particular days. The mechanic made the Johto adventure feel more connected to the player’s real-world routine.

Pokémon Gold and Silver also introduced the Pokégear, which combined functions such as a clock, map, radio, and telephone. Later games expanded the idea with their own day-and-night systems, but Gold and Silver established the main-series foundation. The earlier Red, Green, Blue, and Yellow games did not contain this real-time clock feature.