I now use 2 wall mounted graylabs, but I still have a working LED wrist watch with a timer funcition from the 70s, when I lived overseas I used this watch to time all my paper development, not water proof so I just set it on shelf that I could see it. I have not used in years, wonder if I still find a battery? A kitchen timer will also work if it has glow in the dark hands or a good audio such as a bell or buzzer.