def delay_service(self, t=None):
if len(self._departures) > <NUM_LIT:1>:<EOL><INDENT>agent = heappop(self._departures)<EOL>if t is None:<EOL><INDENT>agent._time = self.service_f(agent._time)<EOL><DEDENT>else:<EOL><INDENT>agent._time = t<EOL><DEDENT>heappush(self._departures, agent)<EOL>self._update_time()<EOL><DEDENT>
Adds an extra service time to the next departing
        :class:`Agent's<.Agent>` service time.

        Parameters
        ----------
        t : float (optional)
            Specifies the departing time for the agent scheduled
            to depart next. If ``t`` is not given, then an additional
            service time is added to the next departing agent.