We have had the same placement arragement with my husband's ex-wife for their children for the past 8 years. We always have them the same days every week. One of those days is Monday.
My husband's ex-wife once asked us if she could keep the kids over Labor Day Weekend, all the way through Labor Day because, "Labor Day falls on a Monday this year." Dude.
Today she asked to keep the kids for camping this coming weekend, all the way through Memorial Day, because, "Memorial Day falls on a Monday this year."
You just can't fix stupid.