It's reported that TLS 1.3 (currently in draft status) can reduce connection setup delays by 30% or approximately 30ms.
How can I configure this on MacOS or iOS?
According to WWDC2017:
TLS 1.3 is not enabled by default
You can enable this on iOS with this provisioning profile
You can enable this on MacOS with this command in Terminal
sudo defaults write /Library/Preferences/com.apple.networkd tcp_connect_enable_tls13 1