Not sure what that waveform represents.
There is a non-deterministic delay between when you press "start" in the IDE and when the audio will actually start. Additionally, the time between when the codec is switched on (and you hear a small click) and when the processed audio started playing is also non-deterministic.
What are you trying to do exactly, that requires to know precisely the amount of time that passes between clicking "start" and the beginning of the sound? If you need accurate timings, you could possibly look at a solution where you start the program, and then you use an event sampled through the Bela digital input (e.g.: a button) to signal the beginning of a very accurate time measurement. In this case, the latency would be constant, down to ±11 microseconds.