CustomtimeHelper.php

<?php
class CustomtimeHelper extends AppHelper {
    public $helpers = array('Time');

    public $days = array(
        1 => 'Lunedì'
        2 => 'Martedì'
        3 => 'Mercoledì'     
        4 => 'Giovedì'
        5 => 'Venerdì'
        6 => 'Sabato'
        7 => 'Domenica'
    );

    public function whatDay($data) {
        return $this->days[$this->Time->format('N', $data)];
    }
}