I know that the posters who hasve already replied will know more than me. But, it might be worth you looking into as a teacher at our school was in exactly the same situation, so she did some digging and found that some LAs had published advice saying that, if a day was nominated for the royal wedding then part timers who normally would not work that day would be entitled to 1/5 of their working week off. Unfortunately, my LA has not published such guidance. However, my colleague went to our union rep, who said that an act of parliament had adjusted the number of days a FT teacher has to be avaiable for work from 195 to 194 this year, so a 0.6 teacher (which she is) needs to be available to work 116.4 days this year as opposed to the usual 117. Therefore, she is entitled to a morning off. Union rep took this to HT, who has now said colleague will, in fact, get a full day off. All happy and joyful. As I say, I am not an expert, but would it be worth a try?