Right so first thing, don't stress about this. If your anything like me you should get it sometime around going for the lizard.
A little hint for using him however, when looking for quest objectives you get gold arrows and a gold circle yes? Well when you are looking for chests or captains or any other location objective, they appear as a white circle/arrow. It cuts down the time you might spend looking for those treasures, and to a degree he can also see through walls. If you pause over where the circle is smallest with the thickest outline he should be able to pin-point a chest thats just in a small room.
Just use him for 30 minutes of cumulative game time and the achievement will pop.
Let's keep cheevin' together!