I bought new machines when I bought this house back 15 years ago. My dryer seems to have a mind of its own on the time. When I turn it on for say cotton, it will start at 40 minutes but if I come back a few minutes later it may say only 20 minutes so it goes by how it feel the moisture of the clothes inside it. My bed sheets seem to take only 15 minutes to dry for me which works great for me. also have it set to tumble off and on for up to 60 minutes in case I forget I've got laundry in the dryer. Nothing worse than having wrinkled clothes, rght?