Place the watermelon pieces on the dehydrator racks spacing them so they do not touch each other. This way they will dry more evenly. I used an Excalibur Dehydrator and my manual says to set the temperature at 135 degrees. Be sure and look at your own dehydrator to see the correct temperature for your dehydrator. The time to dehydrate will always depend on the humidity of the room you are using to dry the product. Today this batch of watermelon took about 9 hours. No chemicals or preservatives.