With MaskedTextBox1
     .Mask = "99 99" : .Text = "0000" : .ReadOnly = True
     .BackColor = System.Drawing.Color.White
     .Font = New System.Drawing.Font("Arial", 12, FontStyle.Bold)
     .Top = 10 : .Left = 10 : .Width = 60
  End With
  With NumericUpDown1
      .Minimum = 0 : .Maximum = 99 * 60 : .Value = 0
      .Top = 10 : .Left = 80 : .Width = 20
  End With

    Private Sub NumericUpDown1_ValueChanged _
    (ByVal sender As System.Object, ByVal e As System.EventArgs) _
    Handles NumericUpDown1.ValueChanged
 
        Static oldvalue As Integer
 
        With MaskedTextBox1
            'Alternativ: oldvalue
            Dim tbval As Integer = _
            CInt(.Text.Substring(0, 2)) * 60 + _
            CInt(.Text.Substring(3, 2))
 
            If oldvalue < CInt(NumericUpDown1.Value) Then
                tbval = System.Math.Min(tbval + 1, 99 * 60)
            Else
                tbval = System.Math.Max(tbval - 1, 0)
            End If
            .Text = Format(tbval \ 60, "00 ") + Format(tbval Mod 60, "00")
        End With
        oldvalue = CInt(NumericUpDown1.Value)
    End Sub