src/main/java/io/reactivex/Observable.java
@CheckReturnValue
    @SchedulerSupport(SchedulerSupport.CUSTOM)
    public final Observable<T> delay(long delay, TimeUnit unit, Scheduler scheduler, boolean delayError) {
        ObjectHelper.requireNonNull(unit, "unit is null");
        ObjectHelper.requireNonNull(scheduler, "scheduler is null");

        return RxJavaPlugins.onAssembly(new ObservableDelay<T>(this, delay, unit, scheduler, delayError));
    }
@CheckReturnValue
    @SchedulerSupport(SchedulerSupport.CUSTOM)
    public final Observable<T> delay(long delay, TimeUnit unit, Scheduler scheduler, boolean delayError) {
        ObjectHelper.requireNonNull(unit, "unit is null");
        ObjectHelper.requireNonNull(scheduler, "scheduler is null");

        return RxJavaPlugins.onAssembly(new ObservableDelay<T>(this, delay, unit, scheduler, delayError));
    }
@ CheckReturnValue @ SchedulerSupport ( SchedulerSupport . CUSTOM ) public final Observable < T > delay ( long delay , TimeUnit unit , Scheduler scheduler , boolean delayError ) { ObjectHelper . requireNonNull ( unit , "unit is null" ) ; ObjectHelper . requireNonNull ( scheduler , "scheduler is null" ) ; return RxJavaPlugins . onAssembly ( new ObservableDelay < T > ( this , delay , unit , scheduler , delayError ) ) ; }
Returns an Observable that emits the items emitted by the source ObservableSource 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.s.png" alt="">
<dl>
<dt><b>Scheduler:</b></dt>
<dd>You specify which {@link Scheduler} this operator will use.</dd>
</dl>

@param delay
the delay to shift the source by
@param unit
the time unit of {@code delay}
@param scheduler
the {@link Scheduler} to use for delaying
@param delayError
if true, the upstream exception is signalled with the given delay, after all preceding normal elements,
if false, the upstream exception is signalled immediately
@return the source ObservableSource shifted in time by the specified delay
@see <a href="http://reactivex.io/documentation/operators/delay.html">ReactiveX operators documentation: Delay</a>
Returns an Observable that emits the items emitted by the source ObservableSource 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 . s . png alt = > <dl > <dt > <b > Scheduler : < / b > < / dt > <dd > You specify which { @link Scheduler } this operator will use . < / dd > < / dl >