src/main/java/io/reactivex/Completable.java
@CheckReturnValue
    @NonNull
    @SchedulerSupport(SchedulerSupport.CUSTOM)
    public final Completable timeout(long timeout, TimeUnit unit, Scheduler scheduler, CompletableSource other) {
        ObjectHelper.requireNonNull(other, "other is null");
        return timeout0(timeout, unit, scheduler, other);
    }
@CheckReturnValue
    @NonNull
    @SchedulerSupport(SchedulerSupport.CUSTOM)
    public final Completable timeout(long timeout, TimeUnit unit, Scheduler scheduler, CompletableSource other) {
        ObjectHelper.requireNonNull(other, "other is null");
        return timeout0(timeout, unit, scheduler, other);
    }
Returns a Completable that runs this Completable and switches to the other Completable
in case this Completable doesn't complete within the given time while "waiting" on
the specified scheduler.
<p>
<img width="640" height="308" src="https://raw.github.com/wiki/ReactiveX/RxJava/images/rx-operators/Completable.timeout.sc.png" alt="">
<dl>
<dt><b>Scheduler:</b></dt>
<dd>{@code timeout} subscribes to the other CompletableSource on
the {@link Scheduler} you specify.</dd>
</dl>
@param timeout the timeout value
@param unit the timeout unit
@param scheduler the scheduler to use to wait for completion
@param other the other Completable instance to switch to in case of a timeout
@return the new Completable instance
@throws NullPointerException if unit, scheduler or other is null