Microwaving a can of soup is not recommended at all, regardless of the duration, as it can be extremely dangerous. Metal cans, including soup cans, are not microwave-safe due to the risk of explosion, as mentioned in the previous responses.
When you microwave a can, the microwaves can cause the liquid inside to heat rapidly and produce steam. This steam builds up pressure inside the sealed can, leading to a high risk of explosion. Even if the can doesn't explode during the microwaving process, it could still rupture or burst open after being removed from the microwave due to the pressure buildup.
The duration of microwaving doesn't determine whether an explosion will occur; it's the presence of metal and the closed container that pose the risk. To heat canned soup safely, it's best to empty the contents into a microwave-safe container before heating. Always follow the recommended guidelines on the soup can or refer to the microwave heating instructions provided by the soup manufacturer. Additionally, ensure you use microwave-safe dishes for any microwave heating to prevent accidents and injuries.