The government plans to call them all to Westminster on 19 October - the day after the make-or-break EU summit that will decide if Britain leaves the EU with a deal just 11 days later.
While the move could technically be voted down by MPs, Downing Street thinks the chances of that happening are slim.
19 October will also see likely thousands of protesters descend on parliament calling for another referendum to give the public a "final say" on Brexit.
And it marks the day when Mr Johnson will be forced to ask the EU to delay Brexit if he has not returned from Brussels with a deal.
He is compelled to because of legislation rushed through the Commons and Lords last month.
But the prime minister has vowed he will not delay the Brexit deadline, and that Britain will leave the EU as planned on 31 October "do or die".
Parliament normally only sits Monday to Thursday, and occasionally on Fridays - which are usually reserved for MPs to head home to their constituencies for events.
Some also work through the weekend dealing with issues in their local area.
Parliament has only sat four times on Saturdays in the last 80 years:
The prospects of Britain leaving the EU with a deal were looking slim after Downing Street accused the EU yesterday of making it "essentially impossible" for a deal to be struck.
Mr Johnson is expected to meet the Irish prime minister on Thursday in a last-ditch effort to break the deadlock.
But Leo Varadkar has said it will be "very difficult" to do so.