Rashi dibbur hamatchil וביום on Vayikra 13:14 says the Torah mentions the apparently superfluous word וביום to teach us that there are times when one (a kohen) doesn’t see and inspect the negah found on someone. For example at nightime (as opposed to the Torah’s daytime) when a chatan celebrates his sheva brachot.
We learn in Yerushalmi Bikkurim 3:3 that Eisav married Machalat. It was really Basmat whom he married but she changed her name because he was machul for all of his sins after having married her. The Gemara uses Eisav as the source to teach that a chatan during his wedding is one occasion in a person’s life during which he receives forgiveness of sins.
If that is true then this chatan metzorah should have already been forgiven for his sins and would not need the Torah to suspend his visit to the Kohen.