code: public final Mono<Tuple2<Long, T>> elapsed(Scheduler scheduler) {
  		Objects.requireNonNull(scheduler, "scheduler");
  		return onAssembly(new MonoElapsed<>(this, scheduler));
  	}
docs: Map this {@link Mono} sequence into {@link reactor.util.function.Tuple2 Tuple2&lt;Long, T&gt;}
  of timemillis and source data. The timemillis corresponds to the elapsed time between the subscribe and the first
  next signal, as measured by the provided {@link Scheduler}.
  
  <p>
  <img class="marble" src="doc-files/marbles/elapsedForMono.svg" alt="">
  
  @param scheduler a {@link Scheduler} instance to read time from
  @return a new {@link Mono} that emits a tuple of time elapsed in milliseconds and matching data