This will depend on the size of your sheet pan (as if it's smaller, you will get a thicker slice which will take longer to cook) and how hot your oven runs. Ours cooked in about 23 minutes and we used a 12x9in (30x22.5cm) size pan. However, check on them at 20 minutes, but they could take up to 25 minutes. You will know they are cooked when they aren't jiggly in the middle any more.