echo "<form method='post'>"; 
echo "<td class='fond' style='text-align:center; font-weight:bold; '><input  name=\"client_a_rappeler\" id='dateRappel' type='text' style='width:75px; height:15px; text-align:center;' value='".date('H:i', strtotime($rech_ent[client_a_rappeler]))."'>&nbsp;&nbsp;<input type=\"image\"  src=\"images/valider_com.png\" style=\"width:15px; background:transparent; border:0;\" align=\"absmiddle\"></td>";
echo "<input type=\"hidden\" name=\"id_rappel\" value=\"".stripslashes($rech_ent[id])."\">";
echo "</form>";


//------------------------------------------------------------------------------------------
///////////////////////////MISE A JOUR DE L'HEURE DE RAPPEL/////////////////////////////////
//------------------------------------------------------------------------------------------
$id_rappel = $_POST['id_rappel'];
$client_a_rappeler = $_POST['client_a_rappeler'];
$conn = db_connect();
//-----------------------------------------------------------------------------------------
//-----------------------------------------------------------------------------------------
	if($client_a_rappeler) {
	$sql = "update ".CLIENTS." set 
	client_a_rappeler = (str_to_date('".$client_a_rappeler."', '%d/%m/%Y %H:%i:%s' ))
	where id = '$id_rappel'";
	$result = @mysql_query($sql, $conn) or die('Erreur SQL !'.$sql.'<br>'.mysql_error());
	
	echo "<meta http-equiv=\"refresh\" content=\"0;url=".$_SERVER['PHP_SELF']."\" />";
}

echo "<form method='post'>";
echo "<td class='fond' style='background:green; color:white; text-align:center; font-weight:bold; '><input name=\"client_a_rappeler\" type='text' onblur='this.form.submit();' style='width:50px; height:10px;' value='".date('H:i', strtotime($rech_ent[client_a_rappeler]))."'></td>";
echo "</form>";


$id_rappel = $rech_ent[id];
$client_a_rappeler = $_POST['client_a_rappeler'];
$conn = db_connect();
//-----------------------------------------------------------------------------------------
//-----------------------------------------------------------------------------------------
	if($client_a_rappeler) {
	$sql = "update cliens set 
	client_a_rappeler = (str_to_date('".$client_a_rappeler."', '%H:%i:%s' ))
	where id = '$id_rappel'";
	$result = @mysql_query($sql, $conn) or die('Erreur SQL !'.$sql.'<br>'.mysql_error());
}

<script type="text/javascript" src="js/jquery-1.7.js"></script>
<link type="text/css" href="css/ui-lightness/jquery-ui-1.7.2.custom.css" rel="stylesheet" />      
<script type="text/javascript" src="js/jquery-ui-1.7.2.custom.min.js"></script>
<script type="text/javascript" src="js/timepicker.js"></script>
<script type="text/javascript">
$(function() {
    $('#dateRappel').datepicker({
    	duration: '',
        showTime: true,
        constrainInput: false
     });
});

</script>
<script>
jQuery(function($){
$.datepicker.regional['fr'] = {
closeText: 'Fermer',
prevText: 'Précédent',
nextText: 'Suivant',
currentText: 'Aujourd\'hui',
monthNames: ['janvier', 'f&eacute;vrier', 'mars', 'avril', 'mai', 'juin',
'juillet', 'ao&ucirc;t', 'septembre', 'octobre', 'novembre', 'd&eacute;cembre'],
monthNamesShort: ['janv.', 'févr.', 'mars', 'avril', 'mai', 'juin',
'juil.', 'août', 'sept.', 'oct.', 'nov.', 'déc.'],
dayNames: ['dimanche', 'lundi', 'mardi', 'mercredi', 'jeudi', 'vendredi', 'samedi'],
dayNamesShort: ['dim.', 'lun.', 'mar.', 'mer.', 'jeu.', 'ven.', 'sam.'],
dayNamesMin: ['D','L','M','M','J','V','S'],
beforeShowDay: $.datepicker.noWeekends,

dateFormat: 'dd/mm/yy',
firstDay: 1,
isRTL: false,
hour:10,
minute:00,
showMonthAfterYear: false,
yearSuffix: ''};
$.datepicker.setDefaults($.datepicker.regional['fr']);
});
</script>

echo "<form action=''>";
echo "<td class='fond' style='background:green; color:white; text-align:center; font-weight:bold; '><input type='text' id='dateRappel' onblur='this.form.submit();' style='width:50px; height:10px;' value='".date('H:i', strtotime($rech_ent[client_a_rappeler]))."'></td>";
echo "</form>";