My last two frags I bought were similar sized to yours, and after a week acclimation period, I started to see a new polyp or two the folloing week. Its been the same rate ever since. I feed reef roids 2x week.
Not all zoas grow at the same rate. I have some (like the Halley Berry) that grows like a weed, and others that are very slow.
I'd say it's safe to assume you should see some growth within a month.