Step #4: The cooking time of the corn on cob in a microwave varies, and is usually based on factors like the microwave type, the freshness of the corn, and other such things. However, the usual time for a ear of corn is seven minutes. If you are placing two, then you might want to increase the time by a minute or two. Once the corn is cooked, take it out of the microwave, and let it sit for around fifteen minutes or so. You can also place it under cold running water and the remaining silk will come up easily.