reactor-core/src/main/java/reactor/core/publisher/Mono.java
public final Mono<T> timeout(Duration timeout, Mono<? extends T> fallback) {
		return timeout(timeout, fallback, Schedulers.parallel());
	}
public final Mono<T> timeout(Duration timeout, Mono<? extends T> fallback) {
		return timeout(timeout, fallback, Schedulers.parallel());
	}
Switch to a fallback {@link Mono} in case no item arrives within the given {@link Duration}.

<p>
If the fallback {@link Mono} is null, signal a {@link TimeoutException} instead.

<p>
<img class="marble" src="doc-files/marbles/timeoutFallbackForMono.svg" alt="">

@param timeout the timeout before the onNext signal from this {@link Mono}
@param fallback the fallback {@link Mono} to subscribe to when a timeout occurs

@return a {@link Mono} that will fallback to a different {@link Mono} in case of timeout