Odd little creatures for sure.My Yellow ones open twice a day that I've seen - once around 2 or 3 in the afternoon for a couple of hours (I think it coincides with the Plank feeding) and then once again around 20-30 minutes after lights out. The pink ones in the 8 gallon I have never seen open but they have been close several times late at night - 1 or 2 in the morningish.

