Of course I know this approach and also others.
First, it's just a stopwatch. Secondly, it is quite cumbersome, time consuming and annoying to install these very extensive blocks in your own app every time. Third, the app only runs in the foreground. Fourth, this is not about the date / time format HH:mm:ss (hours are counted up to 99). Fifth: "When testing this project during development, the emulator will not be able to keep up so use an attached device instead."
The accuracy of the approach is ok (100ms), but my extension works millisecond-precise and I and certainly many others would like a simple, precise and also working in the background solution that counts up and down and also the correct date / time format used.