title: Execute function if and only if a certain amount of time has elapsed since subscription with RxJS
body: <p>I am making an API call through an Observable. If this API call takes more than 200ms, I would like to show a loading screen (by assigning 'true' to my 'loading' variable), otherwise I don't want to show anything, in order to avoid a blink on screen.</p>
  
  <p>Is there an RxJS operator capable of doing this ?</p>
  
  <pre><code>this.apiService.get(`/api/someEndpoint`)
  
  // I hope for something like
  .triggerIfAtLeastThisAmountOfTimeHasElapsed(200, () =&gt; {
    this.loading = true;
  })
  
  .subscribe(response =&gt; {
  
    // Process the response
  
    this.loading = false;
  });
  </code></pre>