参考答案

Private Sub Command1_Click()
    Timer1.Enabled = True
End Sub
Private Sub Timer1_Timer()
    If Val(Text1.Text) = 0 Then
        Text1.Text = ""
        Timer1.Enabled = False
        Text1.SetFocus
    Else
        Text1.Text = Str(Val(Text1.Text) - 1)
    End If
End Sub