Sensor Synchronisation and Frequency Setup

According to this, Isaac SIM should run in real time but with the standalone example

while True: 
        print('Sim {} Real {}'.format(delta world.current_time, delta time.time()))
        # Some synchronous code here
       world.step()

Isaac SIM Seems to override the system time to keep 60Hz physics stepping. Is there a overview document or explanation of how timing works in general?