Our senses have a limited capability to distinguish signals. This might not be surpristing. However, we also have a limited capability to tell in which order signals arrived at our sensory organs.
You should use headphones for this demo.
According to the KIT lecture "Mensch-Maschine-Wechselwirkung in der Anthropomatik (Vorlesung Universität Karlsruhe im KIT, WS 2013/14, J. Geisler)", the time resolution of the human ear is between 2 and 5 ms. This means you will not be able to distinguish the two signlas for less than 2ms. But you will need the signals to be 30-40ms apart to tell which one played first.
I rather need 10ms, but this might also be caused by hardware problems. I doubt
timeout is accurate enough.