src/main/java/io/reactivex/Completable.java
@CheckReturnValue
    @SchedulerSupport(SchedulerSupport.COMPUTATION)
    public static Completable timer(long delay, TimeUnit unit) {
        return timer(delay, unit, Schedulers.computation());
    }
@CheckReturnValue
    @SchedulerSupport(SchedulerSupport.COMPUTATION)
    public static Completable timer(long delay, TimeUnit unit) {
        return timer(delay, unit, Schedulers.computation());
    }
Returns a Completable instance that fires its onComplete event after the given delay elapsed.
<p>
<img width="640" height="413" src="https://raw.github.com/wiki/ReactiveX/RxJava/images/rx-operators/Completable.timer.png" alt="">
<dl>
<dt><b>Scheduler:</b></dt>
<dd>{@code timer} does operate by default on the {@code computation} {@link Scheduler}.</dd>
</dl>
@param delay the delay time
@param unit the delay unit
@return the new Completable instance