30 feet would be closer to 30ms, and is enough to make the feeling of playing the note and the sensation of hearing it start to feel disconnected.
Try this stuff for yourself: take your synth or guitar or bass or what have you, plug it in to your computer, put a simple delay in the path with something like jack_rack, and play. At some point it's going to start feeling weird. Exactly where that point is depends on the person and the nature of the sounds you are making.
Here's another thing you can do: fire up hydrogen and make a pattern which is just a clave or cross stick playing quarter notes at a slow tempo. send the output to both directly to your sound card as well as to an instance of jack rack with a short delay. start increasing the delay time, by 30ms you will hear a clear flam.