At the point “motion to light” latency exceeds 20ms. Under that (time between beginning movement to presenting a matching image onto retina) and your brain doesn’t notice; exceed that and you get motion sickness. Done right, VR/AR is comfortable. Response time is critical, and Apple is among the few capable of managing the entire ecosystem to pull it off (Samsung actually did it first, and that only because graphics guru John Carmack, with the influence of Facebook supporting him, persuaded them to make a key hardware change).