Quick look shows there are at least 10 different shot-timer apps for a phone, only one of which is a pay app. Anyone that has tried these and can recommend one?
I didn't like the app I tried.
Get a boxing timer if you want something that you can set a countdown on and then have a timer (i.e. you could set a 10 second countdown, set your phone down behind you, and then start on the buzzer, then it'll buzz again in 20 seconds).
I have a shot timer but usually just use a regular timer to make sure I'm within the 20 seconds.