src/main/java/io/reactivex/Flowable.java
@CheckReturnValue
    @BackpressureSupport(BackpressureKind.FULL)
    @SchedulerSupport(SchedulerSupport.COMPUTATION)
    public final Flowable<T> delay(long delay, TimeUnit unit, boolean delayError) {
        return delay(delay, unit, Schedulers.computation(), delayError);
    }
@CheckReturnValue
    @BackpressureSupport(BackpressureKind.FULL)
    @SchedulerSupport(SchedulerSupport.COMPUTATION)
    public final Flowable<T> delay(long delay, TimeUnit unit, boolean delayError) {
        return delay(delay, unit, Schedulers.computation(), delayError);
    }
Returns a Flowable that emits the items emitted by the source Publisher shifted forward in time by a
specified delay. If {@code delayError} is true, error notifications will also be delayed.
<p>
<img width="640" height="310" src="https://raw.github.com/wiki/ReactiveX/RxJava/images/rx-operators/delay.png" alt="">
<dl>
<dt><b>Backpressure:</b></dt>
<dd>The operator doesn't interfere with the backpressure behavior which is determined by the source {@code Publisher}.</dd>
<dt><b>Scheduler:</b></dt>
<dd>This version of {@code delay} operates by default on the {@code computation} {@link Scheduler}.</dd>
</dl>

@param delay
the delay to shift the source by
@param unit
the {@link TimeUnit} in which {@code period} is defined
@param delayError
if true, the upstream exception is signaled with the given delay, after all preceding normal elements,
if false, the upstream exception is signaled immediately
@return the source Publisher shifted in time by the specified delay
@see <a href="http://reactivex.io/documentation/operators/delay.html">ReactiveX operators documentation: Delay</a>