What seven diamonds control time in Sonic CD?

The seven diamonds that control time in Sonic CD are the Time Stones. They are hidden in the game’s different zones and form the focus of Dr. Robotnik’s plan to control Little Planet.

Sonic can obtain a Time Stone by entering a special stage after completing an act with enough rings, then destroying six UFOs before time runs out. Each successful special stage awards one stone. Collecting all seven automatically creates a good future in every zone, unlocking the best ending.

The Time Stones are distinct from the Chaos Emeralds, which are the better-known seven gems in the main Sonic series and power transformations such as Super Sonic. Sonic CD uses the Time Stones to support its unique time-travel structure rather than treating them as ordinary power-up jewels.

Their importance extends beyond collection: Robotnik uses their temporal power while converting Little Planet into a fortress. The stones therefore connect the game’s plot, special stages, alternate futures, and multiple endings.