It doesn't really affect who finishes 4th. If the games were played together, City would only need a draw regardless, so it wouldn't really affect how they play. Utd would go all to win, in the hope that City lose.Lots of people suggesting the Swansea-Man City game should be delayed as well, in order to maintain the integrity of the Premier League.
Not really sure I agree with that, as it's not like the title is at stake, only the pressing issue of which Manchester club qualifies for the Champions League. Meh.
But if Utd play later, and City have already got 4th, then Utd might settle for a draw to finish above West Ham or Southampton.