funziona perfettamente:
	Codice PHP:
	
                                    <select name="orario">
                                        <?php
                                        function listaorari($from, $to, $gap) {
                                            $listaorari = array();
                                            $f = substr($from, 0, 2) * 60 + substr($from, 3, 2);
                                            $t = substr($to, 0, 2) * 60 + substr($to, 3, 2);
                                            for ($i = $f; $i <= $t; $i+=$gap) {
                                                $n = intval($i / 60);
                                                $o = str_pad($n, 2, '0', STR_PAD_LEFT) . ':' . str_pad($i - $n * 60, 2, '0', STR_PAD_LEFT);
                                                $listaorari[] = $o;
                                            };
                                            return ($listaorari);
                                        }
                                        foreach (listaorari($ristHrApe, $ristHrChiu, 30) as $hr => $val) {
                                            echo '<option>' . $val . '</option>';
                                        }
                                        //var_export(listaorari($ristHrApe, $ristHrChiu, 30));
                                        ?>
                                    </select>
 
i valori che passo alla funzione li prendo da db.
grazie mille!!