How to improve this

[4x2y]

Try this

Private Sub Timer1_Timer()

    Static HH As Long
    Static MM As Long
    Static SS As Long
    Static TS As Long
    
    TS = (TS + 1) Mod 100
    
    If TS = 0 Then
        SS = (SS + 1) Mod 60
        If SS = 0 Then
            MM = (MM + 1) Mod 60
            If MM = 0 Then
                HH = (HH + 1) Mod 24
            End If
        End If
    End If

 
 Label5.Caption = Right("00" & HH, 2) & ":" & _
                  Right("00" & MM, 2) & ":" & _
                  Right("00" & SS, 2) & ":" & _
                  Right("00" & TS, 2)
 
End Sub