Why have both ye not included the Date part of the question?

PHP Code: 
$query $vbulletin->db->query_read(
    SELECT p_id
    FROM purchases, client
    WHERE id = cid
        AND (cid = 3 OR cid = 4)
        AND date > 123456789
    "
); 
Question is confusing. If you don't want the time element leave out AND date > 123456789
If you want it for all clients and not just 3 and 4 then leave out AND (cid = 3 OR cid = 4)