Timer that can count Hour difference between two DateTime for android

Hi i need help on a timer that can tell the difference of hours or minutes passed after pause, minimize or quit of the android app, i really need help something that is tested and working, im not looking for something that runs in the background, i am looking something that saves the time in playerprefs on quit or pause and resumes the time after opening the app again, i know its about calculating the difference from the old time it was saved and from the datetime.now time, i also tried a script i found but it is not working when combined on exit and minimize operations. the script works when just minimizing and resuming, but once i exit the app. the timex gives different value like it starts from zero again, it also works when i just quit the app and open but when i mix quit app and minimize it does not go well...

import UnityEngine; import System.Collections; import System.DateTime; import System;

static var currentDate : DateTime; static var oldDate : DateTime; static var timex : double; static var temp : long; static var difference : TimeSpan;

var guiStyle : GUIStyle;

function Start() {

 Screen.SetResolution(1280, 720, true);
 Application.targetFrameRate = 29;


  // THIS IS THE ORIGINAL
  //Store the current time when it starts
  currentDate = System.DateTime.Now;


 //Grab the old time from the playerprefs as a long
 temp = Convert.ToInt64(PlayerPrefs.GetString("timeData"));


 //Convert the old time from binary to a DataTime variable
 oldDate = System.DateTime.FromBinary(temp);

// print("oldDate: " + oldDate);

 //Use the Subtract method and store the result as a timespan variable
 var difference : TimeSpan = currentDate.Subtract(oldDate);

// print("Difference: " + difference.TotalSeconds);

 timex = timex + difference.TotalSeconds;

}

}

//////////////////////////////// ///// ON PASUE /////////////// function OnApplicationPause(status : boolean) { ///////////////////////////////////////////////

 /////// ON MINIMIZE /////////

///////////////////////////// if(status == true) { //Save the current system time as a string in the playerprefs class PlayerPrefs.SetString("timeData", System.DateTime.Now.ToBinary().ToString()); // PlayerPrefs.Save();

 Debug.Log("App Minimized");





 }



 /////// ON APP RESUME /////////

/////////////////////////////// if(status == false) {

   //Store the current time when it starts
  currentDate = DateTime.Now;


 //Grab the old time from the playerprefs as a long
 temp = Convert.ToInt64(PlayerPrefs.GetString("timeData"));


 //Convert the old time from binary to a DataTime variable
 oldDate = System.DateTime.FromBinary(temp);

// print("oldDate: " + oldDate);

 //Use the Subtract method and store the result as a timespan variable
 difference = currentDate.Subtract(oldDate);

// print("Difference: " + difference.TotalSeconds);

 timex = timex + difference.TotalSeconds;




  Debug.Log("App Resumed");

 }

} ///////////////////////////////////////////////

function OnApplicationQuit() { //Save the current system time as a string in the playerprefs class PlayerPrefs.SetString("timeData", System.DateTime.Now.ToBinary().ToString()); // PlayerPrefs.Save();

Debug.Log("Quited");

}

function OnGUI() {

   ////// GUI Styles
   guiStyle.fontSize = 38;
   guiStyle.normal.textColor = Color.white;


   ////// DISPLAY TIME B
   GUI.Label(Rect(20,20,300,40), "Time:  " + timex, guiStyle);

}