I called IRCC in September cuz it had been months since I submitted the application and there was no communication.. but the agent told me that once the application arrives at their office the documents are scanned and a temporary number is then assigned.. then they check if its complete.. after it gets assigned to an officer it gets a permanent application number.. which is basically the temporary number (XF000XXXXXX) without the X.. I am not sure how long the scanning process takes..
Hope this helps