At bootup.
It gets the time from the API function GetTickCount, which returns the time since bootup. This little thingie should get you the same values (or very close numbers):
Option Explicit
Private Declare Function GetTickCount Lib "Kernel32" () As Long
Public Sub Main()
Dim ticks As Long
Dim mSecs As Variant
ticks = GetTickCount()
mSecs = ThisDrawing.GetVariable("MILLISECS")
Debug.Print "TickCount: " & ticks
Debug.Print "Millisecs: " & mSecs
End Sub