I have this exact same problem. Several in-game days have passed since I got to this stage of the quest and I have not received a quest update, nor does Merrayil progress the quest when I talk to him. How much time is supposed to pass before the quest updates?
UPDATE AND POSSIBLE SOLUTION:
I suspect that progressing this stage of the quest is tied to the number of hours SLEPT not number of hours PASSED. When I originally got this quest, I went off and explored several areas and completed many side quests during which several days had passed in-game. Despite having gone roughly 4 or more days in-game time, the quest did not progress. However, my character also didn't sleep much during this time. Oh a hunch I put my character to sleep for about 18 hours and when he woke I got a quest notification to pick up the documents from Merrayil.
So to test this I loaded a save from just after receiving part IV of this quest. I immediately put my character to sleep for 24 hours and when he woke the quest progressed. Because of this, I think to progress past this part of the quest, your character has to sleep a certain number of hours.