Android Question Timer keeps freezing my app

Sub Process_Globals
    'These global variables will be declared once when the application starts.
    'These variables can be accessed from all modules.
    Dim Timer1 As Timer
    Timer1.Initialize("Timer1",1000)
    Timer1.Enabled = False
End Sub

Sub Timer1_Tick
Dim minusminute = Minutes.text - 1
Dim minussecond = Seconds.text - 1
  If Seconds.text = 0 OR Seconds.Text = -1 Then
  Minutes.text = minusminute
  Seconds.text = "59"
  Else
  Seconds.text = minussecond
  End If
End Sub

Sub StartStop_Time_Click
   If StartStop_Time.Text = "Start" Then
   Timer1.enabled = True
   StartStop_Time.Text = "Stop"
   Else
   Timer1.Enabled = False
   StartStop_Time.Text = "Start"
   End If
End Sub