Stuckmann did a review on it already and even he didn't give any clarification. I honestly think this one will be whatever everyone feels is best until ANY of the characters reappear.So I found this article.
The Marvel Studios Halloween special staring Gael Garcia Bernal debuts on Disney+ October 7.gizmodo.com
In it they discuss when the Werewolf By y Night special takes place. These are the quotes of note:
io9: "And we don’t even know when this night is. It could have been in the 1940s. It could have been in the future. We don’t really know."
Giacchino: "That’s the great thing. In my mind, it is happening somewhere within the MCU but we purposely never say when, why, how, all of that, because to me, it was just about these characters. Let’s worry about these people for tonight and see what happens."
So seems like there's not going to be anything particularly useful to pinpoint the time placement. It'll probably be down to Disney+ or some obscure hints and details.