Stopwatch in a block

If you see code, there will be a bunch of blocks. If you hit the triangle block, it will start the stopwatch that is displayed at the block? How? It is explained below.

This project uses metaprogramming, introduced at 8.0. Metaprogramming allows you to change elements of a block, and even labels. So, in 8.0, it will be possible to change the labels of a block, therefore making it possible to make that stopwatch.