It depends how long the matches take. For example, one round could take up to 35 minutes because of the 30 +3 rule, while some rounds could take as little as 15 minutes because of the short games. Top cut is a little different, because it is best 2/3, so expect Top Cut to be a bit longer length-wise. With 5 rounds, that means I'm assuming there's about 32-40 players going, so I would see a Top 8, and then expect about an hour and a half more of play.
So I would say if you make Top Cut, expect a 3-4 hour long Cities, but if you don't make it, you should be done in about 2-3 hours.