gistfile1.txt

add_action( 'init', function() {

	global $wpdb;

	$wpdb->query(
		"
		UPDATE {$wpdb->postmeta}
		SET meta_value = ''
		WHERE meta_key IN (
			'out_of_stock_product_preparation_time',
			'out_of_stock_product_preparation_time_min',
			'out_of_stock_product_preparation_time_max'
		)
		AND meta_value = '0'
		"
	);

} );