Bernhard - Hello, I don’t see a way to do what you want, i.e. silence a portion of a URL stream for a specific amount of time upon the user invoking an intent.
When a user enters an audio stream via the “Stream” block, the user leaves your skill and enters the Audio Player component. In this environment, your user can only use built-in commands, e.g. Previous, Next, Pause, Resume, etc., commands you can tweak and customize, but not to the level you describe. Think of Spotify or Amazon Music when imagining how the audio player can works, and/or check this out: