i used a 10mm 12 point ring spanner. was a little tight to get in there, i bent the end of the spanner a bit. if you got enough engine to engine bay wall clearance you might be able to use a long 10mm 12 point socket.
hrmmm... both my 4age and 4agze had the timing pointer sticking from the end of the bolt that hold the tensioner and a star like head onto the tensioner. that star like head doobie is what i put my spanner on to loosen it.