The best way to test if the meringues are done is to taste one. Let it cool and take a bite, it should be dry and crisp. Turn off the oven at this point, and let the meringues cool completely in the oven. If the tasting yielded a soft and chewy meringue, then bake for another 15 to 30 minutes, before cooling in the oven. Store the meringues in an airtight container once cooled, for up to a week.