The frustrating fact of life is that most ovens do not run true to temperature. Your oven may cook faster or slower than your neighbors, and so the best thing you can do is simply keep an eye on your bacon as it cooks. Many ovens also say they are preheated to the indicated temperature when they actually aren't! The specific thickness of your bacon can also cause it to take more or less time in the oven. After you've made your bacon this way a few times, you'll have a good idea of how long it takes for your specific oven.