Comment 6 for bug 1494514

It shouldn't be waiting for a spec. "For ten seconds before the session locks automatically, the display should dim, to warn you that the lock is about to happen, giving you a chance to cancel it. Any input, including volume buttons, should cancel the lock and therefore restore the display." <https://wiki.ubuntu.com/SessionHandling#Lock> And there's nothing in the "Screen Blanking Requirements" to contradict that.