I don’t know the answer to your question, but the time versus temperature changes generates lots of scientific hypothesis on the internet. One thing I learned a long time ago is to ask the “why” question. Are you planning to cook something at the same temperature, such as a protein?  If just baking a potato, I’d turn up the heat.

Unfortunately, you are going to have to experiment to find out. A russet potato is about 80% water so the oven temp needs to be hot enough to have most of that moisture steam away. Thus the usual 375 to 425 degrees F temps you find in cook books for baking a potato. A potato is fully cooked at 210 degrees F and that takes about an hour at 400 degrees. At 250 degrees you might have to bake the potato twice as long just to get the water to heat up and escape. Got a meat thermometer? Try it out and let me know.