the real concern is in doing the initial TLS handshake over an unsecured public WIFI network
No, this isn't a concern due to PKI. (If you disagree with PKI you should stop using the Internet completely.)
If I switch my laptop to use a tethered network via my cellphone prior to hitting an HTTPS website and then switch it back to using the public WIFI after the connection has been established
This isn't possible because you have different IP addresses on those two networks and once a TCP connection has been established on one IP address it can't be moved to a different one.
Interesting... so there no security concern with using HTTPS on a public Wifi? I thought there was some way the connection could be hijacked. Thanks for the response.
No, this isn't a concern due to PKI. (If you disagree with PKI you should stop using the Internet completely.)
If I switch my laptop to use a tethered network via my cellphone prior to hitting an HTTPS website and then switch it back to using the public WIFI after the connection has been established
This isn't possible because you have different IP addresses on those two networks and once a TCP connection has been established on one IP address it can't be moved to a different one.