This is the code I am using - please help me to have it pop up only when the file is truly open and idle.

In This Workbook:

Private Sub Workbook_Open()
On Error Resume Next
Application.OnTime RunWhen, "SaveAndClose", , False
On Error GoTo 0
RunWhen = Now + TimeSerial(0, NUM_MINUTES, 0)
Application.OnTime RunWhen, "SaveAndClose", , True
End Sub

Private Sub Workbook_BeforeClose(Cancel As Boolean)
On Error Resume Next
Application.OnTime RunWhen, "SaveAndClose", , False
On Error GoTo 0
End Sub

Private Sub Workbook_SheetChange(ByVal Sh As Object, ByVal Target As Range)
On Error Resume Next
Application.OnTime RunWhen, "SaveAndClose", , False
On Error GoTo 0
RunWhen = Now + TimeSerial(0, NUM_MINUTES, 0)
Application.OnTime RunWhen, "SaveAndClose", , True
End Sub

Private Sub Workbook_SheetSelectionChange(ByVal Sh As Object, _
ByVal Target As Range)

On Error Resume Next
Application.OnTime RunWhen, "SaveAndClose", , False
On Error GoTo 0
RunWhen = Now + TimeSerial(0, NUM_MINUTES, 0)
Application.OnTime RunWhen, "SaveAndClose", , True

End Sub

In Module 1:

Public RunWhen As Double
Public Const NUM_MINUTES = 5

Public Sub SaveAndClose()
MsgBox "This File Has Been Idle for 5 Minutes" & vbCr & "Please Save and Close Now"

'Reset next idle message
RunWhen = Now + TimeSerial(0, NUM_MINUTES, 0)
Application.OnTime RunWhen, "SaveAndClose", , True
End Sub