Android notification doesn't work properly -

i'm trying send notification @ specific time,set user via timepicker. when run app first time , works, if change time of notification app send immediately. 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 

settings 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();          }     });