Timeline can be ignored. Diagon Alley is a timeline nightmare. Gringott's is in the middle of book 7 so Diagon Alley should be a shuttered burned out war zone. Not pristine with the shops open and a dragon on the roof of Gringott's.
The Man DeLorean and the big eared frog can wonder around and then we can make fun of the nerds who get their panties in a bunch about it. It will be good fun.
And every year heading into Life Day, this guy should wander around the shops.