Just to verify, on the page you link to, that counter at the top will update every new download, right? Because if not, I don't know where to check when you've reached the millionth download.
It doesn't matter. The counter updates/corrects (with steam downloads) every 5 - 10 minutes. The 'competition' is for any unique download for
24 hours afterwards
. So as long as you download once in the
, then you have an entry.
And if you're paranoid, just download the thing once a day.