Here's the test Proper Proof made after developing six Efke PL-100 negatives in 510 Pyro 1:200 for 10, 20, 30, 40, 50, 60 minutes with 1 minute agitation at the beginning and 10-seconds every 10 minutes. Exposed under the enlarger for the minimum time to print through the clear film edge.

Seems clear to me that the 50-minute development is correct. The white cloth on the stairs is Zone VIII.