If the filling is made at the same time as baking, can it be assembled 8 hours later?

It's complicated. There's a lot of whipped cream in the topping, and that tends to weep and collapse if left to sit a long time.
To prevent those problems people add butter or chemical stabilizers.
Bug that's pure whipped cream.
I don't know what would happen with all the other flavorings - with or without additions.
Maybe Posie will have some better advice.