Android Question Using DateTime used in time doesn't triger pause event

Sub Process_Globals
    Dim MyTimer As Timer
End Sub

Sub Globals
    Dim t1 As Long
    Dim MyBeeper As Beeper  'Need audio library
End Sub

Sub Activity_Create(FirstTime As Boolean)
    MyBeeper.Initialize(200, 500) '200 milliseconds, 500 hz
'    MyBeeper.Initialize(Rnd(100,301), Rnd(400,601)) 
'    MyBeeper.Initialize(Rnd(20,101), Rnd(100,201)) 'low
    MyTimer.Initialize("MyTimer",2000)  
    t1=DateTime.Now    
    MyTimer.Enabled=True  
End Sub

Sub Activity_Resume
End Sub

Sub Activity_Pause (UserClosed As Boolean)
End Sub

Sub MyTimer_Tick  
    Dim t2 As Long
    t2=DateTime.Now
    MyBeeper.Beep
   If t2-t1 >=20000  Then  'wait 20 sec
      MyTimer.enabled=False
     MyBeeper.Release
     Activity.Finish
   End If
End Sub
Sub Activity_KeyPress (KeyCode As Int) As Boolean 
    If KeyCode = KeyCodes.KEYCODE_BACK Then    ' Checks if the KeyCode is BackKey
        MyTimer.Enabled=False
        MyBeeper.Release
        Activity.Finish
    End If
End Sub