Keep CountDownTimer running after the app closes

I made a countdown in a service, it works when the app is sending to the background, but when the app to the state "dead" it to the count and restarts when I open again. I need it to continue working even in the dead state, as I need to send notifications when a certain time arrives for example. The code that I'm having this result: BroadcastService.java

package com.example.igord.myapplication2;

import android.app.Service;
import android.content.Intent;
import android.os.CountDownTimer;
import android.os.IBinder;
import android.util.Log;

/**
 * Created by igord on 19/09/2017.
 */

public class BroadcastService extends Service {
    private final static String TAG = "BroadcastService";

    public static final String COUNTDOWN_BR = "com.example.igord.myapplication2";
    Intent bi = new Intent(COUNTDOWN_BR);

    CountDownTimer cdt = null;

    @Override
    public void onCreate() {
        super.onCreate();

        Log.i(TAG, "Starting timer...");

        cdt = new CountDownTimer(60000, 1000) {
            @Override
            public void onTick(long millisUntilFinished) {

                Log.i(TAG, "Countdown seconds remaining: " + millisUntilFinished / 1000);
                bi.putExtra("countdown", millisUntilFinished);
                sendBroadcast(bi);
            }

            @Override
            public void onFinish() {
                Log.i(TAG, "Timer finished");
            }
        };

        cdt.start();
    }

    @Override
    public void onDestroy() {

        cdt.cancel();
        Log.i(TAG, "Timer cancelled");
        super.onDestroy();
    }

    @Override
    public int onStartCommand(Intent intent, int flags, int startId) {
        return START_NOT_STICKY;

    }

    @Override
    public IBinder onBind(Intent arg0) {
        return null;
    }
}

MainActivity

package com.example.igord.myapplication2;

import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;
import android.content.IntentFilter;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import android.widget.TextView;

public class MainActivity extends AppCompatActivity {

    private static final String TAG = "igr";
    private TextView texttempo;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        startService(new Intent(this, BroadcastService.class));
        Log.i(TAG, "Started service");
        texttempo = (TextView) findViewById(R.id.txt_tempo);

    }

    private BroadcastReceiver br = new BroadcastReceiver() {
        @Override
        public void onReceive(Context context, Intent intent) {
            updateGUI(intent); // or whatever method used to update your GUI fields
        }
    };

    @Override
    public void onResume() {
        super.onResume();
        registerReceiver(br, new IntentFilter(BroadcastService.COUNTDOWN_BR));
        Log.i(TAG, "Registered broacast receiver");
    }

    @Override
    public void onPause() {
        super.onPause();
        unregisterReceiver(br);
        Log.i(TAG, "Unregistered broacast receiver");
    }

    @Override
    public void onStop() {
        try {
            unregisterReceiver(br);
        } catch (Exception e) {
            // Receiver was probably already stopped in onPause()
        }
        super.onStop();
    }

    @Override
    public void onDestroy() {
        stopService(new Intent(this, BroadcastService.class));
        Log.i(TAG, "Stopped service");
        super.onDestroy();
    }

    private void updateGUI(Intent intent) {
        if (intent.getExtras() != null) {
            long millisUntilFinished = intent.getLongExtra("countdown", 0);
            Log.i(TAG, "Countdown seconds remaining: " + millisUntilFinished / 1000);
            texttempo.setText(String.valueOf(millisUntilFinished / 1000));
        }

    }
}