WordPress: Custom cron job

vh_cron.php

<?php
/*
Plugin Name: VH Cron
Plugin URI: http://vienhoang.com
Description: Demo for running WP Cron Jobs
Version: 1.0
Author: Vien Hoang
Author URI: http://vienhoang.com
License: GPL2
*/
// Load when wp loads
add_action( 'init', function() {

	$time = wp_next_scheduled( 'vh_cron_hook' );
	wp_unschedule_event( $time, 'vh_cron_hook' );

	// Send an email for first time when nothing is scheduled
	if ( ! wp_next_scheduled( 'vh_cron_hook' ) ) {
		// wp_schedule_event( time(), 'daily', 'vh_cron_hook' );
		// Schedule an singel once
		wp_schedule_single_event( time() + 3600, 'vh_cron_hook' );
	}
} );

add_action( 'admin_menu', function() {
	add_options_page( 'Cron Settings', 'Cron Settings', 'manage_options', 'vh_cron', function() {
		$cron = _get_cron_array();
		$schedules = wp_get_schedules();
		?>
		<div class="wrap">
			<h2>Cron Events Scheduled</h2>
			<?php 
				foreach ( $schedules as $name ) {
					echo "<h3>". $name['display'] . ": " . $name['interval'] . "</h3>";
				}
			?>
		</div>
		<?php
	} );
} );

// Send an email
add_action( 'vh_cron_hook', function() {
	$str = time();

	wp_mail( 'vieninsweden@gmail.com', 'Scheduled with WP_Cron!', "This email was sent as {$str}." );
} );

// Custom cron intervals
add_filter( 'cron_schedules', function( $schedules ) {
	$schedules['two-minutes'] = array(
		'interval' => 120,
		'display' => 'Every Two Minutes'
	);

	$schedules['ten-minutes'] = array(
		'interval' => 600,
		'display' => 'Every Ten Minutes'
	);

	return $schedules;
} );