I think I found it, and the tweet of importance is: "Second, the A50 deadline is a hard deadline - written in the treat itself, the highest form of EU law. And the clock is running down."
Which is true. But it also says: "3. The Treaties shall cease to apply to the State in question from the date of entry into force of the withdrawal agreement or, failing that, two years after the notification referred to in paragraph 2, unless the European Council, in agreement with the Member State concerned, unanimously decides to extend this period."
Is there any reason to believe any member would want to veto an extension? I've not heard of any?
Also, depending on what "unanimous" means here (two parties or 28 parties), total agreement may not be necessary: http://www.consilium.europa.eu/en/council-eu/voting-system/qualified-majority/