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200ms is human reaction time, you can definitely notice it; the rule of thumb is 100ms https://www.pubnub.com/blog/how-fast-is-realtime-human-perce...

Your cite says that < 1s is "for users to feel they are interacting freely with the information". Even a 400ms round trip is well within that limit.

Most, if not all websites require more than one round trip.

HTTP2 can reduce this significantly.