short-days PT work, how do you work out AL?

[Pollaidh]

Hi
I've previously worked 80% FTE (i.e. a 4 day week) and know how annual leave is worked out for that. I am now changing to 70% FTE (3.5 days spread over 4 days, so 2 long days and 2 9-3 days so I can do some of the school run).

What happens if I take a day off, especially if it's one of the short ones? I'm trying to plan a stepped return using annual leave to give shorter weeks but haven't a clue how this works.
Thanks

I work 21 hours over 3 days and annual leave is calculated like this (7hr standard working day at my place of work).

Tuesday - 8.5hrs = 1.2 annual leave
Wed - 7.5hrs = 1.1 annual leave
Thu - 5hrs =0.7 annual leave

Our AL is converted to hours and you take off however many hours you need. so on 4 hour shifts I need to take 4 hours to cover a day, on 7 hour shifts I take 7 hours to cover a day off.

That is written into our contracts, it works well.

Thanks!