I am trying to have a Macro run automatically when a sheet is opened in
excel. Also would I need to put this code in for each spreadsheet designed
for it to run or can just the main sheet trigger the macro to run on all
sheets published or where should I put Sub Auto_Open() in the code below:

Option Explicit
Public Declare Function SetTimer Lib "user32" ( _
ByVal hwnd As Long, _
ByVal nIDEvent As Long, _
ByVal uElapse As Long, _
ByVal lpTimerfunc As Long) As Long

Public Declare Function KillTimer Lib "user32" ( _
ByVal hwnd As Long, _
ByVal nIDEvent As Long) As Long

'==========Public Declarations ==============================
Public TimerID As Long 'Turn On and Off with this ID
Public TimerActive As Boolean 'Is the timer active
Public Const tmMin As Long = 2 'Min time allowed
Public Const tmDef As Long = 5 'Default if min set low
'================================================= ===========

Public Sub ActivateMyTimer(ByVal Sec As Long)
Sec = Sec * 1000
If TimerActive Then Call DeActivateMyTimer

On Error Resume Next
TimerID = SetTimer(0, 0, Sec, AddressOf Timer_CallBackFunction)
TimerActive = True

End Sub

Public Sub DeActivateMyTimer()
KillTimer 0, TimerID
End Sub

Sub Timer_CallBackFunction(ByVal hwnd As Long, ByVal uMsg As Long, ByVal
idevent As Long, _
ByVal Systime As Long)

Application.SendKeys "~", True
If TimerActive Then Call DeActivateMyTimer

End Sub

Function TmMsgBox(sMsg As String, Btn As VbMsgBoxStyle, Optional ShowFor As
Long, _
Optional sTitle As String) As VbMsgBoxResult

If sTitle = "" Then sTitle = Application.Name
If ShowFor < tmMin Then ShowFor = tmDef
ActivateMyTimer ShowFor
TmMsgBox = MsgBox(sMsg, Btn, sTitle)
DeActivateMyTimer

End Function

Sub aTest()
Dim Answer

Answer = TmMsgBox("You have until 12:01 Thursday OK!", vbYesNo +
vbDefaultButton1, , "Data Entry check")

MsgBox Answer

End Sub