Because it's Christmas, of course! Seriously, though, it's common knowledge - especially if you've seen Inception - that time progresses differently within the confines of a dream. Hours can pass by in minutes so, while the characters were facing their untimely deaths in the real world, they had already accepted that they were dreaming at this point so were subsequently beginning to wake up, one by one, from their respective slumbers. You might as well go out whilst enjoying a sleigh ride over London, right?