Returns the blog timezone as a DateTimeZone object

wp-blog-timezone.php

<?php
/*
 * Returns the blog's timezone as a DateTimeZone object
 *
 */
function sh_get_blog_timezone(){
	$timezone = wp_cache_get( 'sh_blog_timezone' );

	if ( false === $timezone || ! ($timezone instanceof DateTimeZone) ) {

		$tzstring =get_option('timezone_string');
		$offset = get_option('gmt_offset');

		// Remove old Etc mappings.  Fallback to gmt_offset.
		if ( !empty($tzstring) && false !== strpos($tzstring,'Etc/GMT') )
			$tzstring = '';

		if( empty($tzstring) && $offset!=0 ):
			//use offset		
			$offset *= 3600; // convert hour offset to seconds

           		$allowed_zones = timezone_abbreviations_list();
			foreach ($allowed_zones as $abbr):
				foreach ($abbr as $city):
					if ($city['offset'] == $offset){
						$tzstring=$city['timezone_id'];
						break 2;
					}
				endforeach;
			endforeach;
		endif;

		//Issue with the timezone selected, set to 'UTC'
		if( empty($tzstring) ):
			$tzstring = 'UTC';
		endif;

		$timezone = new DateTimeZone($tzstring);

		wp_cache_set( 'sh_blog_timezone', $timezone );
	} 

	return $timezone; 
}
?>