Excessive time required to reach dmax

Just getting started with the PiezoDn process. My test for dmax with a clear Pictorico negative, palladium/fo ratio 1:1, exposed in a homemade light box with 12 blue light 20 w bulbs 3" from light source, and Hahnemuhle Platinum Rag paper and developed in ammonium citrate requires 35 minutes for the desired black… This seems awfully long. What has possibly gone haywire. Obviously, I don’t want to push forward until I’m certain this very first, but vitally important step, has been accomplished in a reasonable manner. Thanks in advance for any insights.