Allow the conchas to rise in a warm place until they are almost double in size. Depending on the temperature of your kitchen, this step could take anywhere from 1 to 2 hours. Do not leave them to rise any longer, because if you let them grow too much they will collapse inside the oven. Bake in a preheated oven at 325 degrees for 20 minutes, or until the bottom of the conchas are lightly golden. If you are placing more than one baking sheet in your oven, rotate them after 10-12 minutes.