Custom Number Countdown

// Scheduled Action Hook
function do_decrement( ) {
	$options = get_option($this->plugin_name . '-options');
	
	        if ((int)$options['gcpc_timer_countdown'] > 0) {
	            $options['gcpc_timer_countdown'] = (int)$options['gcpc_timer_countdown'] - 1;
	            update_option($this->plugin_name . '-options', $options);
	        }
}

// Custom Cron Recurrences
function gcpc_schedule_cron_recurrence( $schedules ) {
	$schedules['gcpc_custom_timer_interval'] = array(
		'display' => __( 'Customized by timer_interval option', 'textdomain' ),
		'interval' => 300,
	);
	return $schedules;
}
add_filter( 'cron_schedules', 'gcpc_schedule_cron_custom_recurrence' );

// Schedule Cron Job Event
function gcpc_schedule_cron() {
	if ( ! wp_next_scheduled( 'do_decrement' ) ) {
		wp_schedule_event( time(), 'gcpc_custom_timer_interval', 'do_decrement' );
	}
}
add_action( 'wp', 'gcpc_schedule_cron' );