I don't see the point of maid_day tag.
It's visually just same as maid.
Few pictures (hardly 10 out of 549 tagged) do have "maid day" phrase on them and that's it.
People just carry the tag from pixiv and twitter.
Do we need a tag which tells that these pictures were drawn in a specific date?
There are also similar questionable tags like bikini_day and others.