docs: def set_start(self,time,pad = None):
      """
      Set the start time of the datafind query.
      @param time: GPS start time of query.
      """
      if pad:
        self.add_var_opt('gps-start-time', int(time)-int(pad))
      else:
        self.add_var_opt('gps-start-time', int(time))
      self.__start = time
      self.__set_output()