Krisp Noise Cancellation works by distinguishing human voice from all other sounds. So, with the introduction of the new noise, it will take Krisp at most a few seconds to start cleaning out. You can test how the noise is cleared from your environment with the Test Noise Cancellation feature.
Krisp Background Voice Cancellation feature does not interfere with Noise Cancellation(NC) feature and regardless of having it ON/OFF, you will have the NC feature active.
Krisp works best within a distance of 50 cm. If you are standing farther than that, expect that your voice might be distorted.