Auto Close Workbook After Showing Form For 30 Seconds

I have the following code that displays a form at a user defined time and if the user does not press "Stop" then the workbook saves and closes. The user can press stop then the workbook remains open.

Here is what I have where:
Admin_Auto_Shutdown = Yes or No
Admin_Auto_Shutdown_Time = 3:34pm or user defined time (This doesn't seem to work??)

'Auto Shutdown CloseandSave
If UCase(wb.Worksheets("Admin"). Range("Admin_Auto_Shutdown").Value) = "YES" Then
Application .OnTime TimeValue("Admin_Auto_Shutdown_Time"), "AutoShutdown"
End If

Sub AutoShutdown()

Application.OnTime TimeValue("Admin_Auto_Shutdown_Time"), "AutoShutdown"

Auto_Shutdown_Form.Show

End Sub

Now, my question is about a timer that I can show on a form. When the form is displayed I would like to give the user 30 seconds to press stop (and keep the workbook open) or to press proceed and save and close or to not do anything and the workbook would close and save when the timer reaches zero.

Code for user form which is missing most everything...

Private Sub Halt_Click()
'If user whats to continue without closing
Auto_Shutdown_Form.Hide
End Sub

Private Sub Proceed_Click()
'If user whats to save and close

Auto_Shutdown_Form.Hide

How do I add a timer to this code where it will run this at the end of the timer?

Auto_Shutdown_Form.Hide

Application.DisplayAlerts = False
With ThisWorkbook
.Saved = True
.Close
End With