it happens quickly
I started with 10 female bartlett anthias, and now 4 are clearly males. They get bigger, become very brighter pink with an orangish stripe down the short axis of the body in the middle, but most noticibly the caudal fin elongates and becomes outlined with whitish-pink on top and bottom, and the underbite of the mouth becomes more prominant. Transformation happens suddenly. I did not notice an intermediate stage.
The male behavior also is more aggressive, he is always hearding the females together. If another becomes male, they will fight untill one is kept cornered in a cave. Im my case 3 bachelors stick their heads out and dart in and out for food.
The females remain duller in color. 1 of them will get large and become the dominant female, swimming along side with the dominant male. She bullies the other 5 females.
Ill post pics. They are awesome fish.