which do a lot of printing to serial and repeatedly call the NTP server inside the loop() function.
If you don't want to print, then don't. It is no mystery which function(s) cause Serial data to be print()ed.
If you want to do something once, there is a function where things happen once. Do whatever you want to do once in that setup() function.
In order to keep the time updated I plan on using a check in the loop() function where the GetUTCFromNTP() function will be called once per 24 hours.
So, that was a load of crap up there where you said you wanted to do it ONCE.
Regardless, what you want to do is trivial. Just do it.