A Small Asteroid Just Missed Us

Earth/ Sky News reports an asteroid about the size of a school bus made a close approach to the Earth. Asteroid 2016RB1 passed by around 5:30am if I'm figuring it right, closer than the moon is to us. 

What I'm wondering was when they noticed it? If it was noticed about the time the e-mail notice was sent out, that would mean it was so close they couldn't do anything but think about ways to stop it from hitting our planet.