Notes or blocks on the calendar

Be able to put a note on a day on the calendar. This could either be just for a simple reminder, or block that day from scheduling (for example in the case of a holiday where I do not want to post).

I want to be able to look at the calendar and know a day I planned a post (like a holiday or a launch day). I don’t want to have to create the post, just know I am supposed to.