It is not possible to do with one rule, but the calendar engine can use multiple rules for one event. However, GUI for that is not implemented yet. If you do not mind adding that event as 3 separate events, you can configure them in the following way:frequency = monthly; day of week = Mon..Fri; day of month = 25; frequency = monthly; day of week = Fri; day of month = 24; frequency = monthly; day of week = Fri; day of month = 23;