Quick example of how to schedule a notification in the future using AlarmManager

AndroidManifest.xml

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.cards.notification">

    <uses-sdk
        android:minSdkVersion="17"
        android:targetSdkVersion="17" />

    <application
        android:allowBackup="true"
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name"
        android:theme="@style/AppTheme" >
        <activity
            android:name="com.cards.notification.MainActivity"
            android:label="@string/app_name" >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
        <receiver android:name=".NotificationPublisher" />
    </application>

</manifest>

main.xml

<menu xmlns:android="http://schemas.android.com/apk/res/android">
    <item android:id="@+id/action_5"
        android:title="5 seconds"
        android:showAsAction="never" />
    <item android:id="@+id/action_10"
        android:title="10 seconds"
        android:showAsAction="never" />
    <item android:id="@+id/action_30"
        android:title="30 seconds"
        android:showAsAction="never" />
</menu>

MainActivity.java

package com.cards.notification;

import android.app.AlarmManager;
import android.app.Notification;
import android.app.PendingIntent;
import android.content.Context;
import android.content.Intent;
import android.os.Bundle;
import android.app.Activity;
import android.os.SystemClock;
import android.view.Menu;
import android.view.MenuItem;

public class MainActivity extends Activity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
    }


    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.main, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        switch (item.getItemId()) {
            case R.id.action_5:
                scheduleNotification(getNotification("5 second delay"), 5000);
                return true;
            case R.id.action_10:
                scheduleNotification(getNotification("10 second delay"), 10000);
                return true;
            case R.id.action_30:
                scheduleNotification(getNotification("30 second delay"), 30000);
                return true;
            default:
                return super.onOptionsItemSelected(item);
        }
    }

    private void scheduleNotification(Notification notification, int delay) {

        Intent notificationIntent = new Intent(this, NotificationPublisher.class);
        notificationIntent.putExtra(NotificationPublisher.NOTIFICATION_ID, 1);
        notificationIntent.putExtra(NotificationPublisher.NOTIFICATION, notification);
        PendingIntent pendingIntent = PendingIntent.getBroadcast(this, 0, notificationIntent, PendingIntent.FLAG_UPDATE_CURRENT);

        long futureInMillis = SystemClock.elapsedRealtime() + delay;
        AlarmManager alarmManager = (AlarmManager)getSystemService(Context.ALARM_SERVICE);
        alarmManager.set(AlarmManager.ELAPSED_REALTIME_WAKEUP, futureInMillis, pendingIntent);
    }

    private Notification getNotification(String content) {
           int notificationId = 0;
        NotificationCompat.Builder builder = new NotificationCompat.Builder(this);
        builder.setSmallIcon(R.drawable.ic_launcher_background);
        builder.setContentTitle("THe Test Notification");
        builder.setContentText("This is a background notification by selected time interval.");
        builder.setAutoCancel(true);
        builder.setDefaults(NotificationCompat.DEFAULT_ALL);
        Uri path = RingtoneManager.getDefaultUri(RingtoneManager.TYPE_NOTIFICATION);
        builder.setSound(path);
        NotificationManager notificationManager = (NotificationManager) getSystemService(NOTIFICATION_SERVICE);

        if(Build.VERSION.SDK_INT >= Build.VERSION_CODES.O){
            String channelId = "test";
            NotificationChannel channel = new NotificationChannel( channelId,"This is channel",NotificationManager.IMPORTANCE_DEFAULT);
            notificationManager.createNotificationChannel(channel);
            builder.setChannelId(channelId);
        }
    }

}

NotificationPublisher.java

package com.cards.notification;

import android.app.Notification;
import android.app.NotificationManager;
import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;

public class NotificationPublisher extends BroadcastReceiver {

    public static String NOTIFICATION_ID = "notification-id";
    public static String NOTIFICATION = "notification";

    public void onReceive(Context context, Intent intent) {

        NotificationManager notificationManager = (NotificationManager)context.getSystemService(Context.NOTIFICATION_SERVICE);

        Notification notification = intent.getParcelableExtra(NOTIFICATION);
        int id = intent.getIntExtra(NOTIFICATION_ID, 0);
        notificationManager.notify(id, notification);

    }
}