Live rock starts to decline after 24 hours or so after it has been pulled.
That said, most live rock has been out of the water for several days to a week before it even gets to a store. It still has a ton of good stuff on it if it has been kept warm and moist.
I still prefer the Gulf aquacultured live rock. It's more dense so you pay more even though it's less perpound (if that makes sense). The advantage is they can pull it in the early morning and ship it one day air and get it to you that afternoon. It's not nearly as shapely and as I mentioned, more dense, but the amout of life on it is incredible.