A floater is a common strategy here in the United States.  

The idea behind the floater is to maximize the day by adding a workout that is not part of a standard schedule.  This allows the organizer to program more workouts and limits the downtime Athlete's generally deal with while waiting for their next scheduled heat.

Generally the way it works is, on the morning of the event, Athlete's will have an opportunity to pick a time to do a floater workout.  They will have up until the last hour of the day to complete this workout.