code: public final Flux<T> sampleFirst(Duration timespan) {
  		return sampleFirst(t -> Mono.delay(timespan));
  	}
docs: Repeatedly take a value from this {@link Flux} then skip the values that follow
  within a given duration.
  
  <p>
  <img class="marble" src="doc-files/marbles/sampleFirstAtRegularInterval.svg" alt="">
  
  @reactor.discard This operator discards elements that are not part of the sampling.
  
  @param timespan the duration during which to skip values after each sample
  
  @return a {@link Flux} sampled to the first item of each duration-based window