reactor-core/src/main/java/reactor/core/publisher/Flux.java
public static Flux<Long> interval(Duration delay, Duration period) {
		return interval(delay, period, Schedulers.parallel());
	}
public static Flux<Long> interval(Duration delay, Duration period) {
		return interval(delay, period, Schedulers.parallel());
	}
Create a {@link Flux} that emits long values starting with 0 and incrementing at
specified time intervals, after an initial delay, on the global timer. If demand is
not produced in time, an onError will be signalled with an
{@link Exceptions#isOverflow(Throwable) overflow} {@code IllegalStateException}
detailing the tick that couldn't be emitted. In normal conditions, the {@link Flux}
will never complete.
<p>
Runs on the {@link Schedulers#parallel()} Scheduler.
<p>
<img class="marble" src="doc-files/marbles/intervalWithDelay.svg" alt="">

@param delay  the {@link Duration} to wait before emitting 0l
@param period the period {@link Duration} before each following increment

@return a new {@link Flux} emitting increasing numbers at regular intervals