different for ever zoa and every tank, that's exactly the answer you were looking for right
I find that recently fragged zoas grow faster than an established colony, so both where you cut off of the colony and on the frag new growth seems to come as a result of the healing process. I'v also found that colonies will grow quickly if you give them a natural path towards the light and flow, they don't jump cracks or seperation between rock work very quickly. Anyways that's my two cents