An event has run for certain amount of time. How to find the time for how long this event has run in mysql?
Maybe you can create an evenlog-table. Then inside your event :

BEGIN
  SET @starttime = now();
  ....
  insert into event_log (name, starttime, endtime) values ('myevent', @starttime, now());
END


Like this you'll have a log of all your events over a longer period to compare.