I originally wasn't thinking of using holidays, because I thought that might have reporting implications, but thinking about it again, that may be the best option. I should have specified this before, the factory calendars are needed for planning/manufacturing. Although you are definitely right that it would be easier to use a PWS, we were requested to put these off days in the factory calendar, so I'm not sure if the business would be ok with a PWS, but I will check with them.
From an HR perspective, we will get the time from an inbound interface so I think if nothing else I will use a floating holiday instead of special rules.