They are a smaller carpet than the other two IndoPacific hosting carpet species. I too have seen one at the 24" size but I see them more at the 6"-12" stage. As for growth rates, as stated already, it does depend on how much and how often they are fed, but again they are a little bit slower, in my experience, than haddoni's. To give you an example, I have one brown/yellow tipped specimen that was 5" when I first got it (in 2004), today it is about 15" across and growing rapidly. In fact the last six months the growth rate has really accelerated. I have a green specimen that too was about 5" at purchase, about a year and half it too now is starting to grow fairly rapidly and is approaching 14" or so (hard to tell since they rarely lay flat so you have to guess how big they really are).
In general, smaller anemones than their haddoni and mertensii carpet cousins.