Darkroom Clock is a flexible darkroom timer app suitable for both film and photo development. Build your own development recipes with separate timers for each stage of your development process. The app includes
- fully configurable development recipes.
- darkroom mode (safe to use with B&W photographic paper).
- clear display with all the information you need.
- the whole screen is the start/stop button for the timers
- notifications if you leave the app while a timer is still running

Also the app is free so there is no reason to not download it.