It takes a couple of years for the akadama to break down.
In fall, you should be doing a soil surface cleanup. During the year, you get weeds, and a crust can build up from organic fertilizers. So, in the fall, you go around and remove the top 1/2 to 1 inch of soil. And replace it with fresh. At that time, you will see if the akadama is breaking down, and make a note to repot it in the spring.
You can also look underneath the pot, and if you see there's lots of roots forcing their way out the drain holes, it's time to repot.
Ideally, you should repot just as the akadama begins to break down.