Reset all timezones in wordpress multisite.

gistfile1.txt

<?php

add_action('init', 'maybe_reset_timezone');

function maybe_reset_timezone(){
	
	if (isset($_GET['temp-reset-timezone'])) {
		
		$sites = wp_get_sites();
		foreach($sites as $site){
			switch_to_blog($site['blog_id']);
			update_option('gmt_offset', '');
			update_option('timezone_string', 'America/Chicago');
			restore_current_blog();
		}
		
	}
	
}