If your baking times are significantly shorter or longer than those called for in a recipe, there may be a calibration issue with your oven’s thermostat. This is a very common problem, and almost all ovens – even those that give the impression of precision through digital temperature displays, etc. – will be at least somewhat off in their real-world versus stated temperature reading.
The easiest way to figure out how much your dial temperature is out by is to use an oven thermometer to take a reading inside the oven. For example, set the dial to 350°F, then watch how high the heat climbs before stabilizing. Don’t be surprised if your oven is off by 50°F.
If it’s way off, or if it’s a huge annoyance, you can certainly get an appliance repair person out to look at your oven’s thermostat. If it’s far too cold or far too hot, there may be a serious problem with your oven that needs to be dealt with by a professional.
The easiest short-term solution for a minor temperature discrepancy is to use that same oven thermometer to come up with a conversion chart you can keep handy in the kitchen. If the dial says 400°F but the oven thermometer reads the temperature as 375°F, make a note of it. Measure for other temperatures you’ll likely need, too. If you know your oven’s real temperature, any time a recipe calls for 375°F, you’ll know to set the oven to 400°F to get the right temperature. Use the thermometer to test the heat from time to time, as this can gradually change.
Other things can also affect baking time and the resulting food. When a recipe says to pre-heat the oven, do it. Putting cookies in the oven before the oven is completely heated can prolong the cooking time, and it can also cause issues with the way the leavening agent reacts. Cooking something from frozen instead of fresh, or cooking a larger or smaller amount of food in the oven than the recipe calls for – two loaves of bread instead of one, or vice versa – can change your baking times. Similarly, cooking multiple dishes in the oven at once – especially common around the Christmas holidays – will also change cooking times.
The key here is to get to know your oven, and don’t take what the temperature dial says at face value. Ovens often have quirks like hotspots or heat circulation issues, and it’s by baking with your oven that you learn what to expect from it.