You perceive sensory inputs within a 100ms window as occurring simultaneously. That does not mean that you cannot notice the difference between a 10ms latency and 50ms latency. Your may well perceive variations of latency, just not on a conscious level as a delay. The author asserts that high subliminal latency leads to higher discomfort and decreased productivity. I cannot find any studies on this right now, but it should be pretty straightforward to measure experimentally.