The most dominant 1-2 will grow quickly, probably close to an inch a month. Depending on how bad the dominance is from the top 1-2 fish, the others may not grow as quickly. I had 4 in a tank, and 2 of them grew extremely quickly while the other two barely grew at all. I moved the 2 smaller ones, and they are now growing just as quickly as the others.
But on average, .75" to 1" a month until they get close to 10" or so for a male. Females slightly slower growth after 6" or so.