Try the below code unhides and hides Sheet2.
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Paste all into a module
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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 TimerID As Long
Public TimerSeconds As Single
Sub StartTimer()
Sheets("Sheet2").Visible = True
TimerSeconds = 900 ' 15 mins in seconds
TimerID = SetTimer(0&, 0&, TimerSeconds * 1000&, AddressOf TimerProc)
End Sub
Sub StopTimer()
On Error Resume Next
KillTimer 0&, TimerID
End Sub
Sub TimerProc(ByVal HWnd As Long, ByVal uMsg As Long, _
ByVal nIDEvent As Long, ByVal dwTimer As Long)
Sheets("Sheet2").Visible = False
End Su