2. Precautions for electric oven to make cakes 1, oven preheating Before baking any food, the oven must be preheated to the specified temperature to meet the baking time in the recipe. It takes about 10 minute to preheat the oven. If it is insufficient, it may not reach the specified temperature. If the oven is preheated for too long, it may also affect the service life of the oven.