You can set the blood moons to happen every day in the options while you're loading a game. And in the game, if you have creative turned on, when you press ESC among the things that appear on the right are sliders to change the time of day if you want the horde to happen RIGHT NOW!! or you're having too much fun and want it to last longer, or delay it for a few more game hours if you're not quite ready, you can even set the calendar back a few days if you need even more time or want to play the last blood moon again.