I don't see how anyone can know who leads in any actual voting right now. I thought all the votes were counted at the same time - after the polls close on Nov 2.
Perhaps not. There's been a lot of discussion on this site with regard to counterclaims by Dems and Reps about who's leading in FL early voting. It seems odd that Rove would make a claim with this level of specificity if he didn't know. You'd expect a general claim that the GOP is ahead (unless, as I mentioned, Rove is an evil genius as some claim).
Exit polling AND the GOP has analyzed the party of those who have voted, and made calculations based on that as well.