It's never just one round-trip: the TCP handshake is one round-trip in itself, then there's the TLS handshake needing two addionnal round-trips, and only then comes the HTTP round trip. So the minimum latency you can have to load just the HTML is in fact 4 times the round-trip time. (And I left DNS aside, because the DNS resolution process involves talking to different servers that are thelselves at different distances).