Runtime

Time.timeScale = 0;

Pause time

float timePassedSinceLastFrame = Time.deltaTime;

The time in seconds it took to complete the last frame. Use with Update() and LateUpdate()

float timeSinceStartOfGame = Time.time;

The time in seconds since the start of the game

float physicsInterval =  Time.fixedDeltaTime;

The interval in seconds at which physics and fixed frame rate updates are performed. Use with FixedUpdate()