Android : Async task take to much time to load

Hello i developed app for showing tweets in list.. I am getting all twitter ids from parse.com Code for that.

        ParseQuery<ParseObject> query = new ParseQuery<ParseObject>(
                "Twitter");

        ob = query.find();
        String[] strings = new String[ob.size()];
        // for (ParseObject imageupload : ob) {
        for (int i = 0; i < strings.length; i++) {
            ParseObject object = ob.get(i);

            strings[i] = object.getString("TwitterId");
            // images.add(map);
        }
        if (isNetworkAvailable()) {
            new DownloadTwitterTask(getActivity(), list, images, bar)
                    .execute(strings);
        }

And then i am passing array of twitter ids to async task

@Override
protected String[] doInBackground(final String... screenNames) {
    // String result = null;

    String rString[] = new String[screenNames.length];

    for (int i = 0; i < rString.length; i++) {
        rString[i] = getTwitterStream(screenNames[i]);
        //
    }
    return rString;
}

// onPostExecute convert the JSON results into a Twitter object (which is an
// Array list of tweets
@Override
protected void onPostExecute(String[] result) {
    Twitter twitter = new Twitter();
    for (int i = 0; i < result.length; i++) {
        twitter.addAll(jsonToTwitter(result[i]));

        Collections.sort(twitter, new SimpleDate());

    }

    adapter = new StreamListAdapter(context, twitter);
    list.setAdapter(adapter);
    bar.setVisibility(View.GONE);

}

The problem is that the async task load tweets from all twitter ids and then it displayed in list..

I want to load some tweets and then display it while other tweets are loading in background