title: RxJava2 delay doesn't work
body: <p>I have Repository method:</p>
  
  <pre><code>public Maybe&lt;String&gt; getId(String id){
      return mApiInterface.get().getId(id)
              .subscribeOn(mSchedulerProvider.io())
              .observeOn(mSchedulerProvider.mainThread());
  }
  </code></pre>
  
  <p>I am trying to use this method in cycle with delay:</p>
  
  <pre><code> final ArrayList&lt;String&gt; ids = SharedPreferenceProvider.getIds();
  
      for(final String id:ids) {
          mRepository.get().getId(id)
                  .delay(5, TimeUnit.SECONDS)
                  .subscribeWith(new DisposableMaybeObserver&lt;String&gt;() {
                      @Override
                      public void onSuccess(String s) {  }
  
                      @Override
                      public void onError(Throwable e) { }
  
                      @Override
                      public void onComplete() {  }
                  });
      }
  </code></pre>
  
  <p>But the delay method doesn't work. What am I doing wrong? Sometimes I need a delay between two requests.</p>
  
  <p><strong>Final variant of the decision:</strong></p>
  
  <pre><code>Flowable.zip(Flowable.fromIterable(ids),
                          Flowable.interval(0, 5, TimeUnit.SECONDS).onBackpressureBuffer(),
                          new BiFunction&lt;String, Long, String&gt;() {
                              @Override
                              public String apply(String s, Long aLong) throws Exception {
                                  return s;
                              }
                          }
                  ).flatMapMaybe(new Function&lt;String, MaybeSource&lt;String&gt;&gt;() {
                      @Override
                      public MaybeSource&lt;String&gt; apply(String s) throws Exception {
                          return mRepository.get().testMaybe(s);
                      }
                  }).subscribeWith(new DisposableSubscriber&lt;String&gt;() {
                      @Override
                      public void onNext(String s) {
  
                      }
  
                      @Override
                      public void onError(Throwable t) {
  
                      }
  
                      @Override
                      public void onComplete() {
  
                      }
                  });
  </code></pre>