When I opened up my app today I got pushed to enable 2-step authentication via email. I of course immediately enabled this and authenticated my devices. This is great that they are enabling it in the US. Surprise, though, that there was no announcement about it, or maybe I just completely missed it. You have one minute to enter in the passcode code. Looks like there is also an option to turn on your phone number once you have authenticated.
I see it on my phone but not on the iPad or when accessing via a browser so I question the implementation since it is not for your account but on a device only.
For devices that I was already signed into, I signed out and when I signed back in it required the code. I tested this on iPad and web browser.