When I look at my larvae and see that they are a flatter shape and not cylindrical, I assume that they have gone through metamorphosis.
If I can see the middle stripe starting to develop on an ocellaris, it should be past meta. Clowns will also start swimming more like a clown instead of straight line swimming when they have gone through meta.
Just before meta, you should notice them curling their tails. This is the point that they are developing more intestine area.
If you read "Clownfishes", it explains it but there is nothing like seeing it for yourself to know. Before I saw a clown larvae I was siphoning everything from my tank thinking it may be a clown larvae. When I finally saw one, I finally understood what I had read.