Android notifications not working as expected

I am trying to send a notification at a specific time given by the user through TimePicker

. When I run my app for the first time, it works, but if I change the notification time, my app will send it immediately. I can't figure out why.

MainActivity code:

@Override
protected void onCreate(Bundle savedInstanceState) 
{

    super.onCreate(savedInstanceState);  
    setContentView(R.layout.activity_main);

    pkg=getPackageName();

    //Intent openPage1 = new Intent(MainActivity.this,Impostazioni.class);
    //startService(new Intent(this, serviceNot.class));

    Intent myIntent = new Intent(this , serviceNot.class);     
    AlarmManager alarmManager = (AlarmManager)getSystemService(ALARM_SERVICE);
    PendingIntent pendingIntent = PendingIntent.getService(this, 0, myIntent, 0);
    Calendar calendar = Calendar.getInstance();
    SharedPreferences sharedPref = getSharedPreferences("hour",MODE_PRIVATE);
    notificaH = sharedPref.getInt("hour", 9);
    SharedPreferences sharedPrefS = getSharedPreferences("second",MODE_PRIVATE);
    notificaS = sharedPrefS.getInt("second", 10);
    calendar.set(Calendar.HOUR_OF_DAY, notifyH);
    calendar.set(Calendar.MINUTE, notifyS);
    calendar.set(Calendar.SECOND, 00);

    long time=calendar.getTimeInMillis();
    if(time<System.currentTimeMillis())
    {
        time=time+AlarmManager.INTERVAL_DAY;
    }

    alarmManager.setRepeating(AlarmManager.RTC_WAKEUP, time, AlarmManager.INTERVAL_DAY , pendingIntent);  //set repeating every 24 hours

      

        
        
        
      

    

Setting code:

public class Impostazioni extends ActionBarActivity 
{

 private Switch mySwitch;
 private Switch Sound;
 private TextView ViewOra;
 private Button btnSetOra;
 int ora;
 int minuti;
 static final int TIME_DIALOG_ID=0;
 public TimePickerDialog mTimePicker;
 int notifyH=9;
 int notifyS=00;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_impostazioni);
    mySwitch = (Switch) findViewById(R.id.mySwitch);
    Sound = (Switch) findViewById(R.id.Switch01);
    ViewOra = (TextView) findViewById(R.id.ViewOra);
    btnSetOra = (Button) findViewById(R.id.btnImpostaOra);

    SharedPreferences sharedPref = getSharedPreferences("hour",MODE_PRIVATE);
    notificaH = sharedPref.getInt("hour", 8);
    SharedPreferences sharedPrefS = getSharedPreferences("second",MODE_PRIVATE);
    notificaS = sharedPrefS.getInt("second", 01);

    ViewOra.setText( notifyH + ":" + notifyS);  
    btnSetOra.setOnClickListener(new View.OnClickListener() {

        @Override
        public void onClick(View v) {
            Calendar mcurrentTime = Calendar.getInstance();
            int hour = mcurrentTime.get(Calendar.HOUR_OF_DAY);
            int minute = mcurrentTime.get(Calendar.MINUTE);
            mTimePicker = new TimePickerDialog(Impostazioni.this, new TimePickerDialog.OnTimeSetListener() {
                @Override
                public void onTimeSet(TimePicker timePicker, int selectedHour, int selectedMinute) {
                    ViewOra.setText( selectedHour + ":" + selectedMinute);

                    notifyH=selectedHour;
                    notifyS=selectedMinute;

                    SharedPreferences sharedPref = getSharedPreferences("hour",MODE_PRIVATE);
                    SharedPreferences.Editor prefEditor = sharedPref.edit();
                    prefEditor.putInt("hour",notifyH);
                    prefEditor.commit();
                    SharedPreferences sharedPrefS = getSharedPreferences("second",MODE_PRIVATE);
                    SharedPreferences.Editor prefEditorS = sharedPrefS.edit();
                    prefEditorS.putInt("second",notifyS);
                    prefEditorS.commit();

                }
            }, hour, minute, true);//Yes 24 hour time
            mTimePicker.setTitle("Select Time");
            mTimePicker.show();

        }
    });