As always, however, we must remember that we're not playing with final firmware here, so this may not reflect the performance of the device once it's out.
While that becomes about the same 12 minutes if you divide by Facebook's 900 million users, remember that we're talking about active users here, so Facebook's actual engagement is actually much higher.
"There used to be two staircases and I remember at one point standing here and thinking 'we've knocked all this down and we're still not sure we can make this work', " he said.