So it says you can do it 7 days before arrival, but on the 2nd it wouldn't let me pick the 9th as the arrival date, so I waited until today.
The app's pretty easy, you scan your passport bar code, then take a picture of the info page. Fill in all the usual crap about flight number, hotel address, etc.
Takes about five minutes. Then gives you a QR code you're supposed to show them on arrival; I saved it as a screen shot and we'll see what happens when I land.
I'd rather do that than fuck around trying to fill in a couple of form withs miniscule boxes that you can only complete in microdot, on paper thin enough to remind you of that tracing paper bog roll they used to have when you were young.