It's going to be even faster now.
The Vienna convention basically says that if you're a dispute settlement panel, you first of all look at the words of the texts. If there's any ambiguity in the words of those texts, you can look to supporting evidence. The joint interpretive instrument is intended to be just that. It's an explanation of what the parties' intentions were when they concluded the negotiation, so it has that kind of legal weight such that any panel is going to at least have to consider what is said with respect to the intentions of the party in that document.