Android : runOnUiThread skipped XX frames

I want to set the background of my application dynamically, depending on daytime. This should be checked periodically. Therefore I start this runOnUiThread():

    class BackgroundMainThread implements Runnable {
    // @Override
    public void run() {
        while (!Thread.currentThread().isInterrupted()) {
            try {
                Thread.sleep(1000);
                doBackgroundImage();
                Thread.sleep(30000);
            } catch (InterruptedException e) {
                Thread.currentThread().interrupt();
            } catch (Exception e) {
                Log.e("log_tag2", "Error is " + e.toString());
            }
        }
    }
}

public void doBackgroundImage() {
    runOnUiThread(new Runnable() {
        public void run() {
            try {
                //final FrameLayout framelayout_main_bild = (FrameLayout)findViewById(R.id.framelayout_main);
                //framelayout_main_bild.setBackgroundResource(PictureresID);
                findViewById(R.id.framelayout_main).setBackgroundDrawable(getResources().getDrawable(R.drawable.picture1));
            } catch (Exception e) {

            }
        }
    });
}

I'm running other Threads as well and everything works fine, but only when running this thread the following error occurs:

Skipped 40 frames! The application may be doing too much work on its main thread.

Any idea how to solve that?