How long can you safely leave the oven on with nothing in it?

It is generally safe to leave an oven on for a short period of time, such as when preheating or cooking food. However, it is not recommended to leave an oven on for an extended period of time with nothing in it, as this can pose a fire hazard. It is best to always monitor the oven when it is in use and never leave it unattended for long periods.