Hey there!
This is very common actually. Sitting on the trainer for that long in one position is hard and does cause most of us discomfort. I know @mcneese.chad recommends putting a rocker plate under your trainer so that you have a bit of movement to offset the pressure points on your sit bones. You can check the thread he put out on this here:
Also, simply standing every once in a while or adjusting your position throughout the long workouts can help as well. Other than that, if you don’t have one, investing in a nice chamois for the trainer may help but they are pretty expensive for a little butt pad…