Ahora si funciona Synkronice !!! Dejo el codigo final:
Código PHP:
<select name="hora" size="1" class="negro4">
<option value="">Elegir Hora</option>
<?
$fecha = date("Y-m-d");
$timestamp = strtotime($fecha.' 08:00:00')-900;
$timestamp_limite = strtotime($fecha.' 23:00:00');
do
{
$timestamp += 900;
$hora = date("H:i", $timestamp);
echo "<option value=".$hora.">".$hora."</option>";
} while ($timestamp < $timestamp_limite);
?>
</select>
Muchas gracias
