That would be a nice light combo.
Maybe 6-8 weeks is a little "overstated". What I've found with zoanthids though is that they reach a point of "critical mass" where all of a sudden they ramp up the sprawling rate. It seemed like you had larger colonies (as opposed to the little 6-7 polyps each frags that I always seem to start at
) so I thought maybe you were close. Could be more like a couple months though. At some point though you'll notice it, I'm sure. I find that what happens is of course they all grow at different rates and of course the really nice ones grow the slowest, and they wind up getting swallowed and they disappear. So something to watch out for if you happen to have any favourites.
Here's an interesting observation though, speaking of frag sizes. About 4 months ago or so I picked up a rock covered in blue zoanthids. There must have been close to 100 polyps on it. They did really well for about a month, then started dwindling away. Not real noticeable at first but eventually I was thinking, hey, didn't this rock have more polyps? I found a little clump of 2 polyps floating loose and I glued those to a frag disk. Starting from a frag size of 2 polyps is a pretty meek starting point, but that little frag is now about 10 polyps or so. Meanwhile though, the colony rock is now just a rock. For some reason the colony crashed. I have no idea why - if it's a predation or disease or just generic failure-to-thrive. But the little frag is doing well. It's like they need to be "borne" in your tank to be super hardy - otherwise it's a crapshoot.
Of course this stuff only happens to the nice ones. My reddest zoos crashed earlier this summer too, I have yet to find more of the same variety. Got a couple others "close" to the same degree of bright red but of course it's never quite the same. 30 or so other varieties in this tank and they all spread like weeds (although most were very slow to start), so I don't really think it's a environmental issue, .. just some adapt better or worse than others...