That drawing is intended to show why it can be difficult to generate exact triggering time windows for expected earthquakes. EM Signals are controlled by a variety of forces as are the triggering times.

The drawing was a first approximation. And it will probably be changed or removed. That is because the force buildup time profile before earthquakes is so complicated that I am not sure I can accurately represent it or even fully understand it at this time.

There are daily and monthly fluctuations that look like sine waves in the temporary triggering forces that are affecting the fault zone rock layers. But those forces are difficult to accurately represent in a relatively simple drawing like that.