If the date is custom, return the start datetime with the format %Y-%m-%d %H:%M:%S. Else, returns "".

def get_std_start_date(self):
        """ If the date is custom, return the start datetime with the format %Y-%m-%d %H:%M:%S. Else, returns "". """
        first, _ = self._val
        if first != datetime.min and first != datetime.max:
            return first.strftime("%Y-%m-%d %H:%M:%S")
        else:
            return ""