Codice per ESP8266

/**
 * https://lastminuteengineers.com/esp8266-ntp-server-date-time-tutorial/ - works!
 */
 
#include <NTPClient.h>
#include <ESP8266WiFi.h>
#include <WiFiUdp.h>
#include<SoftwareSerial.h>
SoftwareSerial SUART( 4, 5); //SRX  = DPin-D2; STX = DPin-D1


const char *ssid     = "your-wifi-ssid";
const char *password = "password";

const long utcOffsetInSeconds = 3600;

char daysOfTheWeek[7][12] = {"Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday"};

// Define NTP Client to get time
WiFiUDP ntpUDP;
NTPClient timeClient(ntpUDP, "pool.ntp.org", utcOffsetInSeconds);


//SETUP
void setup(){
  SUART.begin(115200); //enable SUART Port
  Serial.begin(115200);
//wifi
  WiFi.begin(ssid, password);

  while ( WiFi.status() != WL_CONNECTED ) {
    delay ( 500 );
    Serial.print ( "." );
  }

  timeClient.begin();
   
}

//LOOP
void loop() {
  timeClient.update();

  //Serial.print(daysOfTheWeek[timeClient.getDay()]);
  //Serial.print(", ");
  //Serial.print(timeClient.getHours());
  //Serial.print(":");
  //Serial.print(timeClient.getMinutes());
  //Serial.print(":");
  //Serial.println(timeClient.getSeconds());
  // posso remmare i precedenti
  Serial.println(timeClient.getFormattedTime()); // 16:46:32
  //----Send Temp and Humidity signal to NodeMCU via SUART port----
  SUART.print(timeClient.getFormattedTime()); // 16:46:32     

  delay(1000);

}

Codice per arduino

#include<SoftwareSerial.h>
#include <TimeLib.h>

SoftwareSerial SUART(2, 3); //SRX=Dpin-2; STX-DPin-3
//-------------------------
boolean dataSync = false;
char unixString[11];
long unixTime;
//--------------------------------------------
// definisco pin relay
int Relay = 4;
const int OnHour = 10; //SET TIME TO ON RELAY (24 HOUR FORMAT)
const int OnMin = 00;
const int OffHour = 19; //SET TIME TO OFF RELAY
const int OffMin = 00;
//--------------------------------------------
void setup()
{
  Serial.begin(115200); //enable Serial Monitor
  SUART.begin(115200); //enable SUART Port

  pinMode(Relay, OUTPUT);
  digitalWrite(Relay, LOW);

}

void loop()
{
  //--------
  char buffer[40];
   int i = 0;

  // while the ESP output available, push it
  // into the buffer and set the flag true
  while (SUART.available()) {
    buffer[i++] = SUART.read();
    dataSync = true;
  }
  //--------
  //---
  byte n = SUART.available(); //n != 0 means a character has arrived
  if (n != 0)
  {
    char x = SUART.read();  //read character
    Serial.print(x);        //show character on Serial Monitor
    dataSync = true;
  }


  if (dataSync == true) {
    //if ((buffer[0] == 'U') && (buffer[1] == 'N') && (buffer[2] == 'X')) {
      // if data sent is the UNX token, take it
      unixString[0] = buffer[3];
      unixString[1] = buffer[4];
      unixString[2] = buffer[5];
      unixString[3] = buffer[6];
      unixString[4] = buffer[7];
      unixString[5] = buffer[8];
      unixString[6] = buffer[9];
      unixString[7] = buffer[10];
      unixString[8] = buffer[11];
      unixString[9] = buffer[12];
      unixString[10] = '\0';

      /* print the UNX time on the UNO serial
      Serial.println();
      Serial.print("TIME FROM ESP: ");
      Serial.print(unixString[0]);
      Serial.print(unixString[1]);
      Serial.print(unixString[2]);
      Serial.print(unixString[3]);
      Serial.print(unixString[4]);
      Serial.print(unixString[5]);
      Serial.print(unixString[6]);
      Serial.print(unixString[7]);
      Serial.print(unixString[8]);
      Serial.print(unixString[9]);
      Serial.println();
      */
      
      unixTime = atol(unixString);
      // Synchronize the time with the internal clock
      // for external use RTC.setTime();
      setTime(unixTime);
      dataSync = false;
      delay(1000);
    }
    //display internal time
    //digitalClockDisplay();
    
    // ----comando i relay ma non va
    /*
    if(hour() == OnHour && min() == OnMin){
    digitalWrite(Relay,HIGH);
    Serial.println("LIGHT ON");
    }
    
    else if(hour() == OffHour && min() == OffMin){
      digitalWrite(Relay,LOW);
      Serial.println("LIGHT OFF");
    }
    */


    
}

/** display time from internal clock
void digitalClockDisplay(){
  // digital clock display of the time
  Serial.print(year());
  Serial.print("-");
  if (month() < 10) {
    Serial.print('0');
  }
  Serial.print(month());
  Serial.print("-");
  if (day() < 10) {
    Serial.print('0');
  }
  Serial.print(day());
  Serial.print(" ");
  //Serial.print(dayOfWeek[weekday()]);
  Serial.print(' ');
  if (hour() < 10) {
    Serial.print('0');
  }
  Serial.print(hour());
  Serial.print(':');
  if (minute() < 10) {
    Serial.print('0');
  }
  Serial.print(minute());
  Serial.print(':');
  if (second() < 10) {
    Serial.print('0');
  }
  Serial.print(second());
  Serial.println();
}
*/