Clarification about 3 Unavailable days

I work in fragrances and need some clarification about:

"You may select up to 3 days per month that you are not available to work, (Unavailable Days). Two of those days may be used on Sunday and/or Saturday."

When I go into Availability page, all my weekends are grayed out and although Friday looks like I can make unavailable, I actually can't make that day as unavailable in Insite.

My question is, am I able to ask for 1 day off on a Saturday in May to attend a special family event? I see that in MTO, that day is not a key date. It seems I would not be able to request that day in Availability page, but it would need to be done in MTO, right? I wanted to clarify before asking my manager. And currently the site is down so I can't go into AskHR.

This would be my first time requesting any day off on a weekend than my usual Availability days during Mon-Thurs.