How to set a timer in a UserForm Textbox?

I have a code that works perfectly but I have to click on the command button to activate it.

What I want is for the timer to run automaticaly when I open the workboox/UserForm.

When the timer reach 0 seconds, I want the workbook to automatically close using

Workbooks("OUTIL_CRN.xlsm").Save
Workbooks("OUTIL_CRN.xlsm").Close

This is the code that works with a commmand button:

In a module:

Public Const AllowedTime As Double = 1

In the Userform:

Private Sub CommandButton1_Click()

Dim userClickedPause As Boolean ' Gets set to True by the Pause button

Dim stopTime As Date

    userClickedPause = False
    ' If AllowedTime is the number of minutes with a decimal part:
    stopTime = DateAdd("s", Int(AllowedTime * 600), Now) ' add seconds to current time

    ' If AllowedTime is the number of seconds:
    'stopTime = DateAdd("s", AllowedTime, Now) ' add seconds to current time
    Do
        With UserForm1.TextBox1
            .Value = Format(stopTime - Now, "Nn:Ss")
        End With
        DoEvents
        If userClickedPause = True Then
            Exit Do
        End If
    Loop Until Now >= stopTime


End Sub
Private Sub CommandButton2_Click()
    userClickedPause = True
End Sub