In fact, Brode was careful not to call this 'tournament mode', because he said that description means very different things to different players. The way it actually works is that the tournament organiser creates the event, then shares it as a code (presumably much as we do with decklists now) to potential participants. Verifying you're using the correct decks will be handled on the client-side, and the organiser can set a time limit for each round. If everyone gets done early, you all click ready and move on with the next one. Brode made it sound like solutions are also on the way for the esports scene, but I'm excited to try this out.