Which Pokémon games introduced both breeding and a real-time clock?

Pokémon Gold and Silver introduced both Pokémon breeding and a real-time clock.

These Game Boy Color role-playing games were released in Japan in 1999 and internationally in 2000. Their internal clock tracked the time of day and day of the week, affecting events and the Pokémon that could appear.

The games also added the Pokémon Day Care breeding system. Compatible Pokémon left at the Day Care could produce an Egg, which would hatch into a young Pokémon. Ditto made breeding more flexible because it could breed with most Pokémon species outside the No Eggs Discovered group.

Gold and Silver introduced the Johto region and 100 new Pokémon. They also added held items, berries, a split Special stat, and the ability to revisit the Kanto region after completing the Johto adventure. Breeding and time-based events became lasting mechanics in later games.