I don't recall the establishing shot, but from a logic perspective it is unlikely that Jaime let Trystane off the boat, and even less likely that a Dornish boat stuck around in KL for any appreciable time after dropping off a dead princess. As fast as a raven might be, the boat would still be well out of harbor and…

The trick is in freeze-framing the note that Doran gets from Jaimie. He says that he's sending Trystane back to Sunspear on the same boat, as he would not be safe in King's landing. Presumably the note arrives in Dorn about the same time as Trystane.