Patterson is congratulated for his "promotion", however, he has been made a detective which maybe seen as a career advancement but it's not considered a promotion.
Although Patterson eventually deduces the intended victim of the crime, it is pure chance that he does so on the night it is being committed and, as a result, revisits the house on the one night that would make any difference. By that point more than two weeks have passed since Betty Drew's appearance at the police station, and at least two weeks have passed since the case was officially closed.
There are various holes in the plot. If Betty Drew is to be murdered then why establish an alibi that can be checked up on and presumably disproved. Also, if Drew is already in the house why does he and Jill need to hide the sound of him entering the house by the noisy midnight chimes, and further, the sudden starting of the Bartok LP is more likely to wake and alert Betty than mask his entrance into the bedroom.