The only thing I can then tell you, because I don't know what it could be, is that you havent progressed something else. I myself am baffled with how unfair the game is to figure out sometimes. Now I thought I read someone mention going back to the flat at 00:00 triggering it, but that seems way out of place. I will once again, go back to a new save file and this time, I will record EVERY single thing I do to the step. It will take a while, but with enough trial and error, I am determined to figure this out