They can take up to a week or more to open up...especially when you have other denizens disturbing them. My culprits are a decent sized conch, some nassarius snails, and a Falco hawkfish that likes to touch them...a LOT. I have some Midas zoas that got mad when I moved them 3" higher in the tank and refused to open for almost a week until I put them back to the bottom of the tank. Moved Red People eater to the same spot and they never closed. Some are more sensitive, just have lots of patience.