Notify admin user of a manual override of the default UTC timezone setting in WordPress.

notice_date_default_timezone_override.php

<?php

// Notify admin user of a manual override of the default UTC timezone setting in WordPress.
// more details: http://goo.gl/7iqVY
if( date_default_timezone_get() != 'UTC' ) {
	add_action('admin_notices', 'notice_date_default_timezone_override');
}
function notice_date_default_timezone_override(){
    echo '<div class="error"><p>You have a manual override of the default <b>UTC</b> timezone to <b>' . date_default_timezone_get() . '</b> enabled on your install, this will potentially cause conflicts with plugins relying on the default WordPress configuration.</p></div>';
}