The recommended length of time to keep an oven door cracked open while heating it up before putting food inside varies depending on the purpose and type of oven you are using.
Preheating the oven: When preheating the oven, you typically want to allow it to reach the desired temperature before placing food inside. The amount of time to preheat can vary based on the oven's size and the target temperature. In general, it's best to preheat for about 10 to 15 minutes for most home ovens.
Air circulation and steam release: Some recipes or baking techniques, like baking artisan bread or roasting certain meats, may benefit from cracking the oven door during the preheating phase. Leaving the oven door slightly open during the initial minutes can help with air circulation and release excess steam, which may lead to better results for specific recipes. In these cases, leaving the door cracked open for about 5 minutes is often sufficient.
It's important to note that not all ovens are designed to be used with the door open, and doing so may impact the oven's performance, energy efficiency, and safety. Many modern ovens have safety features that might prevent them from operating with the door ajar.
Always follow the manufacturer's guidelines and recommendations for using your specific oven model. If a recipe calls for cracking the oven door, make sure it is explicitly mentioned in the instructions. Otherwise, it's generally best to preheat the oven with the door closed until it reaches the desired temperature, and then place the food inside for cooking or baking.