ESP32-Time-Services-and-SETENV-variable 

How to get time and use SETENV variable for Time Zones and DST

See:
https://github.com/espressif/esp-idf/blob/master/examples/protocols/sntp/README.md
https://www.gnu.org/software/libc/manual/html_node/TZ-Variable.html

Time-zones: https://github.com/nayarsystems/posix_tz_db/blob/master/zones.csv

GMTGMT-1, M3.4.0/1,M10.4.0/2  GMTGMT-1 is the name of the time zone  GMT-1 is 
the abbreviation used when DST is off  1 hour is the time difference from GMT  
GMT is the abbreviation used when DST is on  ,M3 is the third month  .4 is the 
forth occurrence of the day in the month when DST starts  .0 is Sunday  /1 is 
the time in hours when DST starts ,M10 is the tenth month  .4 is the forth 
occurrence of the day in the month when DST ends  .0 is Sunday  /2 is the time 
in hours when DST ends

// Set timezone to British DST setenv("TZ","GMTGMT-1,M3.4.0/01,M10.4.0/02",1);

See: https://www.timeanddate.com/time/zones/ for your country code



Example 

/*H********************************************************************
*
**********************************************************************/
#include <WiFi.h>
#include "time.h"

//************************* DEFINES ************************************

//************************* PROTOTYPES ************************************
String printLocalTime();
int Start_WiFi( const char* ssid, const char* password);

//************************* VARIABLES ************************************
String time_str;
const char* ssid     = "yourSSID";
const char* password = "yourPASSWORD";

/*F********************************************************************
*
**********************************************************************/
void 
setup() 
{ 
	Serial.begin( BAUD );
	Start_WiFi( ssid, password );
	configTime( 0, 0, "pool.ntp.org");
}
/*F********************************************************************
*
**********************************************************************/
void 
loop() 
{
	//See: https://www.gnu.org/software/libc/manual/html_node/TZ-Variable.html
	// CST6CDT, M3.2.0/2:00:00, M11.1.0/2:00:00
	// CST6CDT is the name of the time zone
	// CST is the abbreviation used when DST is off
	// 6 hours is the time difference from GMT
	// CDT is the abbreviation used when DST is on
	// ,M3 is the third month
	// .2 is the second occurrence of the day in the month
	// .0 is Sunday
	// /2:00:00 is the time
	// ,M11 is the eleventh month
	// .1 is the first occurrence of the day in the month
	// .0 is Sunday
	// 2:00:00 is the time
	// Set timezone to British DST
// must include '0' after first designator e.g. GMT0GMT-1, ',1' is true or ON
	setenv( "TZ", "GMT0BST,M3.5.0/01,M10.5.0/02",1); 
	Serial.println( "      UK Time = "+printLocalTime());
	// Set timezone to Eastern Standard Time
	setenv( "TZ", "EST5EDT,M3.2.0/2,M11.1.0", 1);
	Serial.println( "US (EST) Time = "+printLocalTime());
	// Set timezone to Indian Standard Time
	setenv( "TZ", "UTC-05:30", 1);
	Serial.println( "  INDIAN Time = "+printLocalTime());
	// Set timezone to China Standard Time
	setenv( "TZ", "CST-8CDT-8,M4.2.0/2,M9.2.0/3", 1);
	Serial.println( "  CHINA Time  = "+printLocalTime());
	Serial.println();
	delay( 2000 );
}
/*F********************************************************************
*
**********************************************************************/
String 
printLocalTime()
{
	struct tm timeinfo;
	if( !getLocalTime( &timeinfo ) )
	{
		Serial.println( "Failed to obtain time");
		return( "Time Error" );
	}
	//See http://www.cplusplus.com/reference/ctime/strftime/
	char output[80];
	strftime( output, 80, "%d-%b-%y, %H:%M:%S", &timeinfo);
	time_str = String( output );
	return( String( output ));
}
/*F********************************************************************
*
**********************************************************************/
int 
Start_WiFi( const char* ssid, const char* password)
{
	int connAttempts = 0;
	Serial.println( "\r\nConnecting to: "+String(ssid));
	WiFi.begin( ssid, password );
	while( WiFi.status() != WL_CONNECTED ) 
	{
		delay( 500 );
		Serial.print( ".");
		if( connAttempts > 20) 
		return( -5 );
		connAttempts++;
	}
	return( 1 );
}