This video makes it easier to imagine millisecond timing delays.
A pulse of white light flashes at 120BPM quarter-note intervals, synchronized with a pulse of sound in the left channel. This represents the request signal, which is returned by the response in the right channel, an identical sound. A number indicator keeps count for you as it steps up the latency from 0 to 100 milliseconds.
Listen to the audio using headphones, while watching the video display. Relax your eyes/ears and just feel the transmission from the left side of your head to right. You will experience a mental visualization of distance. This distance is measured by the number you see in the unit of milliseconds.