The Ilford pdf for their powder developers gives 9min in full-strength Perceptol for APX100 at EI=50.

I'm not saying that it's right, of course!

I would expect 1+1 or 1+2 to give nicer results, and (sticking my neck out) would give it 11 minutes at 1+1 for my first try.

I would be inclined to expect a low film speed as stated in the post above.