Jack's answer shows you how to use prepared statements correctly. Here is the code to simplify the date calculation using DATEDIFF()
.
$note = "SELECT *, DATEDIFF(NOW(), `date`) AS date_diff
FROM notify
WHERE seeker=:seeker AND donor=:donor
ORDER_BY `date` DESC
LIMIT 1";
$st = $conn->prepare($note);
$st->execute(array(
':seeker' => $_SESSION['email'],
':donor' => $email,
);
$row = $st->fetch(PDO::FETCH_ASSOC);
// do something with $row