The default clock used by pyglet uses the system clock to determine the time (i.e., time.time()). Separate clocks can be created, however, allowing you to use another time source. This can be useful for implementing a separate "game time" to the real-world time, or for synchronising to a network time source or a sound device.
Each of the clock functions are aliases for the methods on a global instance of clock.Clock. You can construct or subclass your own Clock, which can then maintain its own schedule and framerate calculation. See the class documentation for more details.