As our tournaments allow 100% proxies, we are in a somewhat unique position that it is possible to begin using newly-spoiled cards as soon as they are spoiled. How early is too early to allow them?
As an example, we're not going to allow them this weekend because there could be spoilers coming out the day of the tournament. However, our next tournament is four days after the full spoiler is released, so we're considering allowing AKH cards in that tournament.
If you'd like to vote, we have a poll going here.
I must admit, there's some temptation to be aggressive and early in order to have some of the first real-world results with a new set.