RxJava 2. Retry with delay while proceeding other items that are distinct

I have an observable that gets items from a lot of sources:

Source { List<Item> data }

Relationship between sources and items is many-to-many and in different sources items could duplicate themselves. Item is an entity that should be uploaded to server and server does not accept duplicates. To achieve this I merge Sources and distinct their Items by their ids and then upload unique items to server. Like below:

Observable.merge(source1(), source2(), source3())
            .flatMapIterable(sources -> sources)
            .flatMapIterable(source::getItems)
            .distinct(item -> item.getId())
            .flatMapCompletabale(item -> uploadItem(item))

Item uploading could emit several errors and on some of them I should retry to upload item once again later and proceed another items while 'failed' one is waiting for its retrying.

How can I postpone retrying uploading 'failed' item and proceed other items while this one is wating for its try?

Thanks in advance!

I put this function into retryWhen method and get it working.

public class RetryWithDelay implements Function<Observable<? extends Throwable>, Observable<?>> {

private final int maxRetryCount;
private final int retryDelay;
private int retryCount;
private TimeUnit timeUnit;

public RetryWithDelay(final int maxRetryCount, final int retryDelay, final TimeUnit timeUnit) {
    this.maxRetryCount = maxRetryCount;
    this.retryDelay = retryDelay;
    this.timeUnit = timeUnit;
    this.retryCount = 0;
}

@Override
public Observable<?> apply(final Observable<? extends Throwable> attempts) {
    return attempts.flatMap((Function<Throwable, Observable<?>>) throwable -> {

        if (++retryCount < maxRetryCount) {
            return Observable.timer(retryDelay, timeUnit);
        }

        return Observable.error(throwable);
    });
}
}