For me, it doesn't happen until 200 or so turns when I've got 5-6 cities and full caravans between the two.
Sure, it slows a bit, but I'll take that over Elemental circa September 2010.
We could use a visual indicator that the turn calculations are happening though. I've found myself a bit confused when I can't do stuff, only to find all the caravan and pathing movement occurring.