Con este class la mejor forma es redefinir las variables
include("datetimeclass.inc");
$datetimei = new DATETIME();
$datetimei->set_timename("h_inic", "m_inic", "s_inic","p_inic");
$datetimei->set_datetime_byglobal("HTTP_POST_VARS");
$datetimef = new DATETIME();
$datetimef->set_timename("h_fin", "m_fin", "s_fin","p_fin");
$datetimef->set_datetime_byglobal("HTTP_POST_VARS");
para poder hacer en el form
<form name="testdate" method="post" action="example.phtml">
<p><b>test form:</b>
<p>
<?
echo $datetimei->get_select_hours(1, 12, "hora")."<b>:</b>";
echo $datetimei->get_select_minutes(1, "min")."<b>:</b>";
echo $datetimei->get_select_ampm();
echo '<br><br>';
echo $datetimef->get_select_hours(1, 12, "hora")."<b>:</b>";
echo $datetimef->get_select_minutes(1, "min")."<b>:</b>";
echo $datetimef->get_select_ampm();
echo '<br><br>';
echo "<b>Usted ingreso fecha inicial----> ".$datetimei->get_time_entered();
echo '<br><br>';
echo "<b>Usted ingreso fecha final----> ".$datetimef->get_time_entered();
?>
<br><br>
<input type="submit" value="Let's GO" name="go">
</form>
frank