private static function hours_helper($piece) {
$out = new self();
if(strpos($piece, '-') !== False) {
$limits = explode('-', $piece);
$lower = $limits[0];
$upper = $limits[1];
foreach(range($lower, $upper) as $hour) {
$out->add_single(new Hour($hour));
}
} elseif(strpos($piece, ':') !== False) {
$nums = explode(':', $piece);
$out->add_single(new Hour($nums[0], $nums[1]));
} else {
$out->add_single(new Hour($piece));
}
return $out;
}
