Option Explicit
Dim Stunden, Minuten, Sekunden As Byte
 
Private Sub Command1_Click()
 
  Dim Splitted() As String
  Splitted = Split(Text1.Text, ":")
 
  Dim i As Integer
  For i = 1 To 3
      If i = 1 Then Stunden = Splitted(i - 1)
      If i = 2 Then Minuten = Splitted(i - 1)
      If i = 3 Then Sekunden = Splitted(i - 1)
  Next i
 
  Timer1.Enabled = True
 
End Sub
 
Private Sub Form_Load()
  Timer1.Enabled = False
  Timer1.Interval = 1000
End Sub
 
Private Sub Timer1_Timer()
 
  If Sekunden > 0 Then
     Sekunden = Sekunden - 1
  Else
     If Minuten > 0 Then
        Minuten = Minuten - 1
        Sekunden = 59
     End If
  End If
 
  If Minuten = 0 And Stunden > 0 Then
     Stunden = Stunden - 1
     Minuten = 59
  End If
 
  Text1.Text = TimeSerial(Stunden, Minuten, Sekunden)
 
  If Stunden = 0 And Minuten = 0 And Sekunden = 0 Then
     Timer1.Enabled = False
     MsgBox "Zeit ist um !", vbInformation, "Meldung"
  End If
 
End Sub

var = var - "00:00:01"