[Android]AppWidgetProviderでAlarmManager#setRepeatingがリピートしない

Question

自作ウィジェットを作っております。１秒おきにカウントダウンをしたいのでAppWidgetProvider内でAlarmManager#setRepeatingを呼び出し更新させています。テスト環境はNexus 5X Android 6.0です。以下コードになります。

AppWidgetProvider

public class MyWidget extends AppWidgetProvider {

    public static final String IMAGE_CLICKED = "ImageClicked";
    public static final String COUNTDOWN_OPERATION = "CountdownOperation";
    public static boolean DOES_RUN_COUNTDOWN;
    public static final String UPDATE_TIMETABLE_OPERATION = "UpdateTimeTableOperation";
    private final int INTERVAL_COUNTDOWN = 1000;
    private final int INTERVAL_UPDATE_TIMETABLE = 1000 * 60 * 10;

    @Override
    public void onUpdate(Context context, AppWidgetManager appWidgetManager, int[] appWidgetIds) {

        DOES_RUN_COUNTDOWN = false;

        RemoteViews remoteViews = new RemoteViews(context.getPackageName(), R.layout.bustimetable_widget);
        ComponentName watchWidget = new ComponentName(context, BusTimetableWidget.class);

        remoteViews.setOnClickPendingIntent(
                R.id.imageView_bus,
                getPendingIntentBroadcast(context, IMAGE_CLICKED)
        );

        appWidgetManager.updateAppWidget(watchWidget, remoteViews);
    }

    @Override
    public void onReceive(Context context, Intent intent) {
        // TODO Auto-generated method stub

        AppWidgetManager appWidgetManager = AppWidgetManager.getInstance(context);
        RemoteViews remoteViews = new RemoteViews(context.getPackageName(), R.layout.bustimetable_widget);
        ComponentName watchWidget = new ComponentName(context, BusTimetableWidget.class);

        if(intent.getAction().equals(IMAGE_CLICKED)){

            if(DOES_RUN_COUNTDOWN){
                DOES_RUN_COUNTDOWN = false;
                Toast.makeText(context, "IMAGE_CLICKED: " + DOES_RUN_COUNTDOWN, Toast.LENGTH_LONG).show();
                cancelCountdownAlarm(context);

            } else {
                DOES_RUN_COUNTDOWN = true;
                Toast.makeText(context, "IMAGE_CLICKED: " + DOES_RUN_COUNTDOWN, Toast.LENGTH_LONG).show();
                setCountdownAlarm(context);
            }

        } else if(intent.getAction().equals(UPDATE_TIMETABLE_OPERATION)){

            Toast.makeText(context, "UPDATE_TIMETABLE_OPERATION: " + Calendar.getInstance().getTime(), Toast.LENGTH_LONG).show();

        } else if(intent.getAction().equals(COUNTDOWN_OPERATION)){

            remoteViews.setTextViewText(R.id.textView_fore_count, "n: " + count++);
            // Toast.makeText(context, "COUNTDOWN_OPERATION: " + Calendar.getInstance().getTime(), Toast.LENGTH_SHORT).show();

        }

        appWidgetManager.updateAppWidget(watchWidget, remoteViews);
        super.onReceive(context, intent);
    }

    private void setCountdownAlarm(Context context) {
        PendingIntent operation = getPendingIntentService(context, COUNTDOWN_OPERATION);
        AlarmManager alarmManager = (AlarmManager)context.getSystemService(Context.ALARM_SERVICE);
        long firstTime = System.currentTimeMillis() + 1000 * 3;
        alarmManager.setRepeating(AlarmManager.RTC, firstTime, INTERVAL_COUNTDOWN, operation);
    }

    private void cancelCountdownAlarm(Context context){
        AlarmManager alarmManager = (AlarmManager) context.getSystemService(Context.ALARM_SERVICE);
        PendingIntent operation = getPendingIntentService(context, COUNTDOWN_OPERATION);
        alarmManager.cancel(operation);
    }

    protected PendingIntent getPendingIntentService(Context context, String action) {
        Intent intent = new Intent(context, getClass());
        intent.setAction(action);

        return PendingIntent.getService(context, 0, intent, 0);
    }
}

widget_info.xml

<?xml version="1.0" encoding="utf-8"?>
<appwidget-provider
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:initialKeyguardLayout="@layout/bustimetable_widget"
    android:initialLayout="@layout/bustimetable_widget"
    android:minHeight="40dp"
    android:minWidth="40dp"
    android:previewImage="@drawable/bus_image"
    android:resizeMode="horizontal|vertical"
    android:updatePeriodMillis="0"
    android:widgetCategory="home_screen"/>

Manifest

            <intent-filter>
                <action android:name="android.appwidget.action.APPWIDGET_UPDATE" />
                <action android:name="CountdownOperation" />
                <action android:name="UpdateTimeTableOperation" />
                <action android:name="ImageClicked"/>
            </intent-filter>

ImageViewのクリックに応じてカウントダウンをスタート、キャンセルする形を取っています。
現状、ImageViewのクリックには即時反応するのですが、カウントダウンは更新が呼ばれていません。おそらくAlarmManagerの使い方が間違っているのではないかと思うのですが、ご指南よろしくお願いします。