The longer you leave the injected / inoculated wood, the better the quality. Ideally 2 years waiting time is commercially accepted, however one may let it be longer time for better resin formation of the man made inoculated wood.
7 years injected
Someone forwarded a question what if the inoculated tree is left for 20 years? I have not seen the real sample yet, i don’t comment.
Someone told if the tree is strong enough, the healing process will eventually recover the injured part and overtime the resin formation will disappear through recovery process. This makes the agarwood (resinous heartwood) disappear if not harvested in a proper time.
The other saying which contradicts the above-mentioned statement…. Agarwood trees are stupid species, when they become injured or infected with mould, a dark resinous heartwood is form. Prior to infection, the heartwood is relatively light and pale coloured; however, as the infection progresses, the tree produces a dark aromatic resin in response to the attack, which results in a very dense, dark, resin embedded heartwood. As a result, the resinous heartwood formation blocks the nutrient passage in Xylem and Phloem. So, Agarwood trees are silly plant, blocking its own nutrient passages in the wound, commiting suicide. In this case, Agarwood will remain in the trees, eventhough the trees die naturally.
Gaharu 沉香 Agarwood 
The last paragraph is incorrect. Heartwood has no “living function” except for support (like human spinal chord and the skeletal system). It doesn’t transport water and nutrients. These functions are left for Xylem and Phloem. Hint, hint…. Agarwit applies the same principles.
….to be exact the resinous heartwood refers to “resinous wood”, correcting the error.
Does cultivated agar wood produce sinking wood over time?
Definately will….but reaaly a long time process…