i have used parodinal at 1:50 for 16 minutes 20C. one full minute of slow inversions then 3 inversions at 4, 8, and 12 minute mark. i was photographing in snow so the concentration was good for getting good highlights and very close to box speed. i have experienced that parodinal is prone to fogging as time increases so i tend to keep times under 20 min. i'm developing for diffusion. hope this helps.