If there is nothing inside the microwave, it is generally safe to leave it on for the duration of the timer. However, it is important to note that the microwaves will still be active and circulating within the microwave cavity. These microwaves are designed to interact with water molecules, which is how they generate heat and cook food.
In the absence of food or any other substance to absorb the microwaves, they may reflect off the walls of the microwave cavity. This reflection can cause the microwaves to bounce around, potentially leading to standing waves or hot spots within the microwave. These hot spots can cause damage to the microwave itself and may pose a fire risk if left unattended for an extended period.
Therefore, it is generally recommended to avoid running a microwave empty for prolonged periods. If you accidentally leave it on, it is best to stop the microwave as soon as possible to prevent any potential issues. Additionally, it's a good practice to consult the specific instructions and safety guidelines provided by the manufacturer of your microwave to ensure proper and safe usage.