The time it takes for an oven to lower its temperature depends on several factors, including the type of oven, the initial temperature, the target temperature, and the environment in which the oven is placed. However, I can provide some general information on how ovens cool down.
When you turn off an oven, it starts to lose heat immediately, but the rate of cooling is not constant. Ovens are typically well-insulated to retain heat, so they don't cool down rapidly like a stovetop burner. The cooling rate will be faster during the initial phase and gradually slow down as the temperature approaches the ambient temperature of the surrounding environment.
As a rough estimate, an oven can cool down by approximately 100°F (37.8°C) in the first 10 to 15 minutes after being turned off. Beyond that, the cooling rate will slow down, and it might take an additional 20 to 30 minutes or more to cool from 400°F (204.4°C) to 250°F (121.1°C).
Please note that these estimates can vary based on the specific oven model, insulation, and other environmental factors. If you need precise temperature control for a particular recipe, it's best to use an oven thermometer or a smart oven with accurate temperature monitoring.