I finally managed to build the Pomodoro app into the latest PineTime firmware (which btw. got updated to 1.15.0 in the meantime).
The DFU zip file got uploaded using companion tool called Siglo, which usually takes a couple of minutes.
How happy I was to find out it worked just like that, first time!
See the end result here.
Interval times are configurable now and default to 25 minutes of work and 5 minutes of break. Just like in your typical pomodoro timer.
What’s next is to track minor bugs and improve the user experience a little bit, but I am already using the app quite often during the day.