Not usually, but sometimes. Each ear of corn will cook at approximately the same time, however when you add more volume to your pressure cooker, you do increase the time to pressure and this time is cook time. So, if you are cooking 1-6 ears of corn, you wouldn't need to change the time. For larger amounts, like 7-10 ears of corn, you may want to consider decreasing your pressure cook time down by 1 minute. The only limitations to how many ears you can cook is how much corn you can fit and that depends on the size of your pressure cooker.