My international NPD client has what I believe is a common challenge internationally. They have the ability to elect to exchange a regular working day (tied to their holiday's) for a weekend work day to extend their "holiday". This is being done on a business unit level. The project planning, needs to account for these changes as their project timelines/durations are very controlled in order to manage CAPEX and OPEX expenses & Product stage gate timelines accross a large organization. These "exchanges" of working day for a holiday vary from year to year.