date_default_timezone_set(timezone)

<?php
   //setting the timezone
   tz = 'Indian/Mahe';     date_default_timezone_set(tz);
   timeZone = date_default_timezone_get();
   print("Default timezone: ".timeZone);
?>

Default timezone: Indian/Mahe

<?php
   //setting the timezone
   tz = 'Asia/Kolkata';     date_default_timezone_set(tz);
   //Retrieving the default timezone
   timeZone = date_default_timezone_get();
   print("Default timezone: ".timeZone);
   print("\n");

   //Comparing the timezone with ini-set timezone 
   if (strcmp($timezone, ini_get('date.timezone'))){ 
      print('Script timezone and ini-set timezone are not same.'); 
   } else { 
      print('Script timezone and ini-set timezone are same.'); 
   } 
?>

Array
Default timezone: Asia/Kolkata
Script timezone and ini-set timezone are same.

$dateSrc = '2007-04-19 12:50 GMT';
$dateTime = date_create( $dateSrc);;
$DateTimeZone = date_timezone_get ( $dateTime );

echo 'Return timeZone is '. timezone_name_get ($DateTimeZone);
echo "\n";

# Using second function.
$dateTime = new DateTime($dateSrc);
$DateTimeZone = $dateTime->getTimezone ();

echo 'Return timeZone is '. timezone_name_get ($DateTimeZone);

Return timeZone is America/Denver
Return timeZone is America/Denver