Finally completed chapter 4! Whilst I've been trying to stick to "as written" as much as possible to make this a fair test, I reckon it's pretty much impossible to run chapter 4 without adding some supplemental material, even if it's only downtime activities. As written, several days to a week pass between each faction quests, and adventurers don't like to sit around doing nothing. I found the quests quite good for gradually advancing the plot, but I think the players felt they were too light on combat. Whilst it was attempting to make the location feel exotic, there are a lot of unpronounceable names in this chapter, and far too many NPCs for the players to keep track of.
Time for chapter 4: about 15 hours.
By the time the players entered the drowned city they were itching for a fight, but things still start out very talky. It might be more fighty for an "evil" party fighting their way past the Allsight faction guards. The players experienced their first taste of ruidium corruption. I'm not sure about the exhaustion mechanic, it's not one of my favourite 5e rules.