I can't use it on windows because the extension isn't on the file's name. Even typing it myself it won't run. :/
Tho on android i got it going no problem. 

Could also have an option to silence the timer sound effect. Outside of that i really loved the aesthetic, was needing something like this. Nice work!

This looks like a very neat and interesting little timer. Interesting way of winding it up too. 

The thing that annoys me of it however is the the sound it makes witch each second ticking down, even when unfocused. Maybe have like a mute button or a volume adjusting option could make it more convenient.