(PECL libevent >= 0.0.1)
event_add — Add an event to the set of monitored events
   event_add() schedules the execution of the event
   when the event specified in event_set() occurs or in at least the time
   specified by the timeout argument. If
   timeout was not specified, not timeout is set. The
   event must be already initalized by event_set()
   and event_base_set() functions. If the
   event already has a timeout set, it is replaced by
   the new one.
  
eventValid event resource.
timeoutOptional timeout (in microseconds).
   event_add() returns TRUE on success or FALSE on error.