Dim gCount As Date
'Updateby20140925
Sub Timer()
    gCount = Now + TimeValue("00:00:01")
    Application.OnTime gCount, "ResetTime"
End Sub
Sub ResetTime()
Dim xRng As Range
Set xRng = Application.ActiveSheet.Range("E1")
xRng.Value = xRng.Value - TimeSerial(0, 0, 1)
If xRng.Value <= 0 Then
    MsgBox "Countdown complete."
    Exit Sub
End If
Call Timer
End Sub