how does flatMapDelayError flow working in flux to make parallel call

Question

I want to call two differnt down stream service and have zip the results. I have tired the below, want to confirm is there is any other best approach that we have or how does flatMapDelayError functioning? i am not blocking the call anywhere. does this two calls will happen parallelly or the second call will wait for the first one? i want both the call should happen parallelly

Flux<EmpAddressDetail> empAddDetail =  getTimeoutDuration()
            .flatMapDelayError(duration -> timeoutWrappedEmpDetailFlux(Service.getemeEmpAddress(empno),
                    duration, Exception.ErrorCode.TIMED_OUT), CONCURRENCY, PREFETCH);

Flux<Employee> empInfo= getTimeoutDuration()
        .flatMap(duration -> mapEmpTypes(empTypes)
                .map(empTypedata -> Tuples.of(duration, empTypedata)))
        .flatMapDelayError(durationEmpTuple -> getEmpdetails(empno, durationBusinessTuple.getT1(), durationEmpTuple.getT2())
                .filter(empdetails -> requestTypes.contains(empdetails.getType()))
                .doOnNext(empdetails -> empdetails.setEmpId(empno)), CONCURRENCY, PREFETCH);

return Flux.zip( empInfo, empAddDetail ).map(tuple -> {
    Employee emp = tuple.getT1();
    emp.setAddressDetail(tuple.getT2());
    return emp;
});