. FWIW, I would leave them in there at least 12 hrs. Their yolk sacks will supply nutrients and depending on the aeration/ water level, they shouldn't tumble very much. That way you let them situate before exposing them to an acclimation. But I don't have any personal experience and I'm positive Ace gave you great advice. For the sake of future experimenters, what did you choose? Please keep us posted on your moves so others might learn. Did you already have a tank set up for them? Why did you remove them prematurely? I had little success with them accepting a false long spine urchin but others have. What route did you go? What foods are you planning to feed once their yolks wear off?