codice:
$query = 
"SELECT  
       Nick,Stato,Simbolo,Status,
       UNIX_TIMESTAMP(Ultima) AS Ultima,
       Ultima_Arma,Salute 
FROM 
       pgu 
WHERE 
       Nick='$user_id' 
AND
       (NOW()-UNIX_TIMESTAMP(Ultima)>600)";

$result = mysql_query($query, $db) or print(mysql_error());
if (mysql_num_rows($result)<=0) {
       echo "troppo presto";
       return FALSE;
}
$wer = mysql_fetch_array($result);
...