求教“倒计时”时间差的问题！！！急急

wzl118

该代码工作时显示剩余时间，但所用时间我不知道用什么代码去控制，并能显示在弹出窗口中。代码如下：Private Sub Command60_Click()
Dim a As Long
a = Val("10:00:00")
b = Val(Me.y)
MsgBox "使用时间：" & a - b & "分钟，请计时！"



'DoCmd.Close
End Sub

Private Sub Form_Load()
Me.TimerInterval = 0
    If Nz(Me.h) = 0 And Nz(Me.m) = 0 And Nz(Me.s) = 0 Then Exit Sub
Me.TimerInterval = 1000
End Sub
Private Sub Form_Timer()
If Me.s = 0 Then
        Me.s = 59
        If Me.m = 0 Then
            Me.m = 59
            Me.h = Me.h - 1
        Else
            Me.m = Me.m - 1
        End If
    Else
        Me.s = Me.s - 1
    End If
    Me.y = Nz(Me.h, 0) & ":" & Nz(Me.m, 0) & ":" & Nz(Me.s, 0)
    If Nz(Me.h) = 0 And Nz(Me.m) = 0 And Nz(Me.s) >= 1 And Nz(Me.s) <= 5 Then Beep
    If Nz(Me.h) = 0 And Nz(Me.m) = 0 And Nz(Me.s) = 0 Then
    Me.TimerInterval = 0
    MsgBox "时间已到，比赛结束!"
    DoCmd.Close
    End If
End Sub