You might be convinced, though, that you know when. You might think the event cannot be Friday because if the night doesn’t happen by Thursday, then Friday would not be a surprise.
Because Friday is out of the picture, the event could not be on Thursday either for similar reasoning. If the show doesn’t happen by Wednesday, then Thursday would not be a surprise. By the same reasoning, you might conclude that the event cannot occur on Wednesday, Tuesday, or Monday.
So there may be no doubt in your mind that you have solved this riddle and that there will be no open mic, but you couldn’t be further from the truth.