How is overtime being calculated?
WorkTimes calculates your overtime per weekday and only for those weekdays having at least one record with type working time. The corresponding regular hours are determined by the weekday of the start time of the record.
If you don't create a record in the case of reduce your overtime, WorkTimes will not reduce you total amount of overtime automatically. This has to be done manually by adding a new record with kind "Overtime" and a negative duration.