That is disputed, as you will know, because the EU has a complex approval procedure. But even if we accept that they did, it matters not a jot. The text of Article 16 talks about actions as small in scope and of limited duration as possible with a view to keeping as much of the protocol in operation as possible. So an invocation lasting a few hours would be not problem at all and fully in keeping with the protocol. In fact the possibility multiple invocations of Artucle 16 over time is clearly part of the safeguards.

Some of the Brexiteer wing seem to think Article 16 is some sort of legal hand grenade that demolishes the protocol once and for all. It is not.