Ditto.
Many non-indos take a long time. However I have had the rarer indo morphs take a long time time also.
First and foremost you have to take into account your tank parameters such as Ca/Alk, lighting, salinity etc.... Then you have to consider if you are feeding correctly (max 3x week). There is no true magic component that answers the question. There is a fragging tutorial posted showing that the best method to propagate Acans is to cut the polyps in half.