Verifiy NTP server update - at start
Having read the NTPClientLib code, I would say that the first sync is not even attempted for 1 second after NTP.begin() is called anyway.


You could do this

void startNTP() {
    NTP.begin("pool.ntp.org", 2, true);
    delay(2000); // there seems to be a 1 second delay before first sync will be attempted, delay 2 seconds allows request to be made and received
    int counter = 2;
    while ( !NTP.getLastNtpSync() &amp;&amp; counter &lt;=2) {
        Serial.print("NTP CHECK: #");
        Serial.println(counter);
        counter +=1;
        delay(1000);
    };
    NTP.setInterval(clockUpdateInt); // in seconds
}


or, you could do this

void loop() {
    // code that doesn't rely on valid time
    //
    // lets say this bit of code requires sync'd time
    if (NTP.getLastNtpSync()) {
        // this will only run once NTP has been sync'd at least once
    }
    // more code that doesn't require sync'd time
}


Now, you may want to check how long time hasn't been sync'd for in your code and do something if it's been too long