Just checked my notes from last year. Made a top tier fro a wedding cake as fruitcake.
I use an electronic, stand-alone pressure cooker with a rack to elevate the cake out of the water. Alton Brown's recipe is nice as a fruitcake. We also liked an amaretto cherry pecan fruitcake.
Once the batter was prepared, I baked it in the pressure cooker on high for 35 minutes. I used a 7 inch springform pan. The layers were 2 inches high and weighed about 2 pounds.
Put two cups of water in the pressure cooker. Place a rack or overturned bowl in the pressure cooker to raise the cake above the water. Lay strips of foil in a cross shape on the rack to use as a lifter to remove the hot cake from the cooker. Cover the cake pan with an inverted plate to prevent excess water from getting in the cake.
I made a note to try bake even strips the next time. That was only because it domed and i was making a layer cake.
If you use a different size pan or make it thicker, you will need to add more time. However, it cuts the bake time down to minutes instead of hours.
Also note - if you are making many fruitcakes, baking in a traditional oven will save you time since you can fit many more. A pressure cooker only holds one at a time.