The time it takes to preheat an oven varies by oven, and some newer models have quick-preheat features. However, it usually takes about 10-15 minutes to preheat an oven to 350ºF, with an additional increase of 5 or so minutes per every 100 degrees above 350ºF. Therefore, preheating an oven to 400-450ºF or above typically takes about 15-20 minutes.