The cake is done when a toothpick inserted into the center comes out without raw batter on it. (celebratingsweets.com)
Put a toothpick into the middle and it should come out without moist batter on it. (mysuburbankitchen.com)
Make sure you test the muffins, do the toothpick test, just put a toothpick in the middle of one and pull it out if it clean then they are done, if got batter on it cook a few minutes longer. (seductioninthekitchen.com)