Código PHP:
function dif_dias ($day, $month, $year)
{
$target = mktime(7,0,0,$month,$day,$year);
$diff = $target - time();
$days = ($diff - ($diff % 86400)) / 86400;
$diff = $diff - ($days * 86400);
$hours = ($diff - ($diff % 3600)) / 3600;
$diff = $diff - ($hours * 3600);
$minutes = ($diff - ($diff % 60)) / 60;
$diff = $diff - ($minutes * 60);
$seconds = ($diff - ($diff % 1)) / 1;
$restante = "";
$month = $days-30;
if ($month <=0 ){
$month =0;
}else{
$month = 1;
}
if ($days > 0 )
$restante = $restante . $days . " días ";
if (($hours >= 0) && ($restante != ""))
$restante = $restante . $hours . " hrs. ";
if (($minutes >= 0) && ($restante != ""))
$restante = $restante . $minutes . " min.";
if (($seconds > 0) && ($restante ==""))
$restante = $restante . $seconds . " seg.";
if ($restante ==""){
echo "0 dias 0 hrs. 0 min.";
}else{
echo $restante;
}
return $restante;
}