If you put food in the microwave for 30 seconds versus putting it in for five minutes but canceling after 30 seconds, the result will generally be the same. In both cases, the food will have been microwaved for 30 seconds.
Microwaves work by emitting electromagnetic waves that excite water molecules within the food, generating heat. When you set a specific time on the microwave, it will continue emitting microwaves until the set time elapses or until you manually stop the process.
In the first scenario, where you put the food in the microwave for 30 seconds, it will receive continuous microwave exposure for the entire duration, heating the food for that period.
In the second scenario, where you set the microwave for five minutes but cancel after 30 seconds, the food will still receive microwave exposure for the first 30 seconds. When you cancel the microwave, it immediately stops emitting microwaves, so the food will not receive any further heating beyond that point.
Therefore, whether you microwave the food for 30 seconds or set it for a longer time and cancel after 30 seconds, the cooking time and the resulting level of heating will be the same—30 seconds.