I created this timer app for my son. It's free to use if you find it helpful. I optimized it for phone/tablet. Let me know if you have questions/suggestions: bradley.w.wright (at) gmail.com
The 5, 10, 20, & 30 buttons willl give you a timer for the chosen number of minutes.
The 10/3 button will give you a timer that alternates between 10 minute study periods (green) and 3 minute breaks (blue). This is supposed to work well for kids (and probably adults as well) with ADHD.
Toggle the hoot/no hoot button to turn the hoot every 30 seconds on/off. The idea of the hoot is that my kid likes owls and also, it should help with refocusing if your mind has wandered.