It's the other way round but I use a time timer[1] to give me a visual indication of how much time is left. I usually put around 40 min & extend by 15~30min if I want to focus more. It doesn't have a big clicky button, but I find physically rotating the dial satisfying.
I've also experimented with iOS timer to stop playing music after the set time is up and that worked well as a non intrusive reminder too.