invalid dates and ad-hoc dates

I need help with a couple of things if possible please:

– Tried using the ‘invalid dates’ functionality but it isn’t working.

– Also l wanted to add the odd ad-hoc day (like one Saturday a month) but can’t see anyway of doing this. The only solution l can see is to add in Saturday’s as a working day then block out those l don’t want.

Thank you in advance

The page I need help with: [log in to see the link]