You can assemble your spanakopita up to 8 hours before you plan to bake it. Store the trays of appetizers loosely covered in the fridge. You may need to add a few extra minutes to the baking time. You can also bake your triangles, then store them in the refrigerator for up to 3 days. Reheat these snacks in the oven at 350 degrees F until they're crispy.