I am not an expert on this but I wanted to share a thought. I think that the morphing process has to do with a few factors
1. Age of fish
3. Size of tank and health of Environment
I think that it is very odd how sometimes you will find an emperor that is 3inches in length and midway through the morph and other times a 6 inch specimen that has barely started. I truly believe that the more stressors that are on the animal the more likely it will take a very long time to complete the change. Almost like some kind of Darwinian Concept of retaining jeuvenile coloration for camouphlage in an uncertain environment.