I hope that it was clear that I was being somewhat tongue-in-cheek about the Monday thing.
Back to the original topic again! This is not a vocab coincidence, but a grammatical one:
I’m working today.
I’m at home on Friday.
It doesn’t make sense to say “on today” or “今日に” in either language, nor would you leave out on/に in “on Friday”/“金曜日に”. It feels unusual when the preposition/particle usage for named times happens to line up between languages.