The Time Manager (menu: Edit > Project Settings > Time) lets you set a number of properties that control timing within your game.
|Fixed Timestep||A framerate-independent interval that dictates when physics calculations and FixedUpdate() events are performed.|
|Maximum Allowed Timestep||A framerate-independent interval that caps the worst case scenario when frame-rate is low. Physics calculations and FixedUpdate() events will not be performed for longer time than specified.|
|Time Scale||The speed at which time progresses. Change this value to simulate bullet-time effects. A value of 1 means real-time. A value of .5 means half speed; a value of 2 is double speed.|
The Time Manager lets you set properties globally but it is often useful to set them from a script during gameplay (for example, setting Time Scale to zero is a useful way to pause the game). See the page on Time and Framerate Management for full details of how time can be managed in Unity.