Place fruit puree in oven & leave the door ajar at all times. Rotate cookie sheets every few hours. Very little attention is required for fruit leather but it takes from 24 to 29 hours drying time. I let mine in day & night & don't even get up during the night - but maybe once to check on it. Altho you must be sure it's not too warm; too cool during the unattended hours is better than too hot. After about 20 hours or after leather is firm enough, lay a piece of saran wrap over the top & flip it over, then remove the top wrap, so the leather can dry on that side too. Repeat this several times during the last few hours drying time. P.S. The bottom of the lower cookie sheet will seem almost hot to the touch - then rotate!